Transceiver in a two-way satellite system

ABSTRACT

An apparatus for transmitting and receiving signals over a two-way satellite communication system is disclosed. A receiving unit receives data from a user terminal. A transmitting unit is coupled to the receiving unit and transmits the data to an antenna. The data is transmitted over a return channel that is established over the satellite to a hub; the hub has connectivity to a packet switched network.

CROSS-REFERENCES TO RELATED APPLICATION

This application is related to, and claims the benefit of the earlierfiling date of U.S. Provisional Patent Application No. 60/197,246, filedApr. 14, 2000, entitled “System and Method for Providing Control of aTwo-way Satellite System,” the entirety of which is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a satellite communication system, andis more particularly related to a two-way satellite communication systemproviding access to a packet switched network.

2. Discussion of the Background

Modern satellite communication systems provide a pervasive and reliableinfrastructure to distribute voice, data, and video signals for globalexchange and broadcast of information. These satellite communicationsystems have emerged as a viable option to terrestrial communicationsystems. As the popularity of the Internet continues to grow inunparalleled fashion, the communication industry has focused onproviding universal access to this vast knowledge base. Satellite basedInternet service addresses the problem of providing universal Internetaccess in that satellite coverage areas are not hindered by traditionalterrestrial infrastructure obstacles.

The Internet has profoundly altered the manner society conductsbusiness, communicates, learns, and entertains. New business models haveemerged, resulting in the creation of numerous global businesses withminimal capital outlay. Traditional business organizations have adoptedthe Internet as an extension to current business practices; for example,users can learn of new products and services that a business has tooffer as well as order these products by simply accessing the business'swebsite. Users can communicate freely using a wide variety of Internetapplications, such as email, voice over IP (VoIP), computer telephony,and video conferencing, without geographic boundaries and at nominalcosts. Moreover, a host of applications within the Internet exist toprovide information as well as entertainment.

Satellite communication systems have emerged to provide access to theInternet. However, these traditional satellite-based Internet accesssystems support unidirectional traffic over the satellite. That is, auser can receive traffic from the Internet over a satellite link, butcannot transmit over the satellite link. The conventional satellitesystem employs a terrestrial link, such as a phone line, to send data tothe Internet. For example, a user, who seeks to access a particularwebsite, enters a URL (Universal Resource Locator) at the user station(e.g., PC); the URL data is transmitted over a phone connection to anInternet Service Provider (ISP). Upon receiving the request from theremote host computer where the particular website resides, the ISPrelays the website information over the satellite link.

The above traditional satellite systems have a number of drawbacks.Because a phone line is used as the return channel, the user has to tieup an existing phone line or acquire an additional phone line. The userexperiences temporary suspension of telephone service during theInternet communication session. Another drawback is that the set-top boxhas to be located reasonably close to a phone jack, which may beinconvenient. Further, additional costs are incurred by the user.

Based on the foregoing, there is a clear need for improved approachesfor providing access to the Internet over a satellite communicationsystem. There is a need to minimize costs to the user to therebystimulate market acceptance. There is also a need to permit existingone-way satellite system users to upgrade cost-effectively. There isalso a need to eliminate use of a terrestrial link. Therefore, anapproach for providing access to a packet switched network, such as theInternet, over a two-way satellite communication system is highlydesirable.

SUMMARY OF THE INVENTION

According to one aspect of the invention, an apparatus for transmittingand receiving signals over a two-way satellite communication systemcomprises a receiving unit that is configured to receive data from auser terminal. A transmitting unit is coupled to the receiving unit andconfigured to transmit the data to an antenna. The data is transmittedover a return channel that is established over the satellite to a hub;the hub has connectivity to a packet switched network. The abovearrangement advantageously minimizes costs to the user, therebystimulating market acceptance.

According to another aspect of the invention, a system for exchangingsignals over a two-way satellite network comprises an indoor receivingunit (IRU) that is configured to receive data from a user terminal. Anindoor transmitting unit (ITU) is selectively coupled to the receivingunit and configured to transmit the data. An outdoor unit (ODU) iscoupled to the IRU and ITU and is configured to receive the data fortransmission over a return channel that is established over thesatellite to a hub. The hub has connectivity to a packet switchednetwork. This approach permits existing one-way satellite system usersto upgrade cost-effectively.

According to one aspect of the invention, a receiver apparatus forreceiving signals over a two-way satellite communication systemcomprises a receiving unit that is configured to receive data from auser terminal. A power supply is configured to provide power to thereceiving unit. The receiving unit is selectively connected to atransmitting unit that is configured to transmit the data over a returnchannel that is established over the satellite to a hub. The abovearrangement advantageously provides compatibility with existingequipment.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a diagram of a two-way satellite communication systemconfigured to provide access to a packet switched network (PSN),according to an embodiment of the present invention;

FIG. 2 is a diagram of the return channel interfaces employed in thesystem of FIG. 1;

FIG. 3 is a diagram of the transceiver components utilized in the systemof FIG. 1;

FIG. 4 is a diagram of the architecture of a network operations center(NOC) in the system of FIG. 1;

FIGS. 5 a and 5 b show a diagram of the system interfaces and packetformats, respectively, that used in the system of FIG. 1;

FIGS. 6A-6P are diagrams of the structures of exemplary packets used inthe system of FIG. 1;

FIG. 7 is a flow chart of the return channel bandwidth limiting processutilized in the system of FIG. 1;

FIG. 8 is a flow chart of the auto-commissioning process utilized in thesystem of FIG. 1;

FIG. 9 is a flow chart of the antenna pointing operation associated withthe auto-commission process of FIG. 8;

FIG. 10 is a diagram showing the scalable architecture of the system ofFIG. 1; and

FIG. 11 is a diagram of a computer system that can support theinterfaces for two-way satellite communication, in accordance with anembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, for the purpose of explanation, specificdetails are set forth in order to provide a thorough understanding ofthe invention. However, it will be apparent that the invention may bepracticed without these specific details. In some instances, well-knownstructures and devices are depicted in block diagram form in order toavoid unnecessarily obscuring the invention.

The present invention provides a two-way satellite system thateliminates the requirement for a phone line to support two-wayapplications and provides the ability to use dedicated high-speed returnchannels. The high-speed satellite broadcast system supports a UniversalSerial Bus (USB) ready transceiver (i.e., adapter) that may be attachedto a personal computer (PC) transmit data and to receive the satellitebroadcast through a single antenna.

Although the present invention is discussed with respect to protocolsand interfaces to support communication with the Internet, the presentinvention has applicability to any protocols and interfaces to support apacket switched network, in general.

FIG. 1 shows a two-way satellite communication system that is configuredto provide access to a packet switched network (PSN), according to anembodiment of the present invention. A two-way satellite communicationsystem 100 permits a user terminal, such as a PC 101, to access one ormore packet switched networks 103 and 105 via a satellite 107. One ofordinary skill in the art would recognize that any number of userterminals with appropriate functionalities can be utilized; e.g.,personal digital assistants (PDAs), set-top boxes, cellular phones,laptop computing devices, etc. According to an exemplary embodiment thepacket switched networks, as shown, may include the public Internet 105,as well as a private Intranet 103. The PC 101 connects to a transceiver109, which includes an indoor receiver unit (IRU) 109 a, an indoortransmitter unit (ITU) 109 b, and a single antenna 111, to transmit andreceive data from a network hub 113—denoted as a network operationscenter (NOC). As will be explained in greater detail with respect toFIG. 4, the hub 113 may include numerous networks and components toprovide two-way satellite access to PSNs 103 and 105. The user terminal101 can transmit data to the NOC 113 with an uplink speed of up to 128kbps, for example, and receive data on the downlink channel with speedsof up to 45 Mbps. As shown in the figure, the NOC 113 has connectivityto Intranet 103 and the Internet 105, and supports a multitude ofapplications (e.g., software distribution, news retrieval, documentexchange, real-time audio and video applications, etc.), which may besupplied directly from a content provider or via the Internet 105.

Essentially, the system 100 provides bidirectional satellitetransmission channels. The downlink channel from NOC 113 to thetransceiver 109 may be a DVB (Digital Video Broadcast)-complianttransport stream. The transport stream may operate at symbol rates up to30 megasymbols per second; that is, the transport stream operates at bitrates up to 45 Mbps. Within the transport stream, the IP traffic isstructured using multiprotocol encapsulation (MPE). One or more MPEGPIDs (Program IDs) are used to identify the IP (Internet Protocol)traffic. In addition, another PID is used for the framing and timinginformation.

The uplink channel from the transceiver 109 to the NOC 113 includesmultiple carriers, each operating at speeds of 64 kbps, 128 kbps, or 256kbps, for example. Each of these carriers is a TDMA (Time DivisionMultiple Access) stream, which employs several transmission schemes.Upon first use of user equipment, tools may be employed to provideinitial access and to request further bandwidth as required. Thespecific bandwidth allocation scheme may be designed to ensure maximumbandwidth efficiency (i.e., minimal waste due to unused allocatedbandwidth), and minimum delay of return channel data. Further, thescheme is be tunable, according to the mixture, frequency, and size ofuser traffic.

The two-way satellite system 100 can be implemented, according to anexemplary embodiment, based upon an existing one-way broadcast system.The conventional one-way broadcast system utilizes a terrestrial linkfor a return channel. In contrast, the two-way satellite system 100obviates this requirement. However, the user terminal 101 may optionallyretain the dial-up connection as a back-up connection to the Internet105.

According to one embodiment of the present invention, the two-waysatellite system 100 offers the following services to the user terminal101: digital package multicast delivery, multimedia services, andInternet access. Under the digital package delivery service, the system100 offers a multicast file transfer mechanism that allows anycollection of PC files to be reliably transferred to a collection oftransceivers. The IP multicast service carries applications, such asvideo, audio, financial and news feed data, etc., for broadcast to thetransceivers (e.g., 109). As already discussed, the system 100 provideshigh-speed, cost-effective Internet access.

To receive the broadcast from system 100, PC 101 may be equipped with astandard USB (Universal Serial Bus) adapter (not shown) and a 21-inchelliptical antenna 111. The system 100, according to one embodiment,uses a Ku- (or Ka-) band transponder to provide up to a 45 MbpsDVB-compliant broadcast channel from the NOC 113. Further, dataencryption standard (DES) encryption-based conditional access can beutilized to ensure that the PC 101 may only access data that the PC 101is authorized to receive.

In accordance with an embodiment of the present invention, the USBadapter may be attached to IRU 109 a, which is connect to ITU 109 b. Thedata is passed from the PC 101 to the USB adapter of the PC 101, whichformats the data for transmission and provides both the control and datafor the ITU 109 a. The ITU 109 a sends the data to an outdoor unit(ODU), which includes antenna 111, at the appropriate time for the datato be transmitted in TDMA bursts to equipment at the NOC 113. In thisexample, when averaged across a year, each two-way transceiver isexpected to have a bit-error rate less than 10⁻¹⁰ more than 99.5% of thetime whereby a single bit error causes the loss of an entire frame. Thetransceiver is more fully described later with respect to FIG. 3.

FIG. 2 shows the return channel interfaces that are employed in thesystem of FIG. 1. The architecture of the two-way system 100 is an openarchitecture, which advantageously affords information providers controlover their content. Specifically, the two-way system 100 providesinterfaces to information providers at the NOC 113 and standardApplication Programming Interfaces (APIs) on the host PC 101. The userterminal 101 is loaded with host software and drivers to interface withthe transceiver 109 and to control antenna 111. The PC 101, in anexemplary embodiment, runs the following operating systems: Microsoft®Win98 Second Edition and Windows 2000. The PC software may provideinstruction and support for installation and antenna pointing (includingautomatic registration and configuration), package delivery, and driversthat are used by the native TCP/IP (Transmission ControlProtocol/Internet Protocol) stack to support standardapplications—including Winsock API with multicast extensions and webbrowsers.

The two-way system 100 supports the exchange of digital packages to oneor more receiving PCs. The term “package”, as used herein, refers to anydata (including electronic documents, multimedia data, softwarepackages, video, audio, etc.) which can take the form of a group of PCfiles. Package delivery is used by an information provider to sendpackages to receiving PCs; for example, the delivery of digitizedadvertisements to radio and TV stations.

To prepare a package for transmission, a publisher (i.e., contentprovider) may merge the package's files into a single file using theappropriate utility (e.g., PKZIP), and subsequently load the packageinto the NOC 113 using an off-the-shelf file transfer mechanism (e.g.,TCP/IP's file transfer protocol (FTP)). The publisher may control thefollowing parameters associated with the package: addresses of thedestination PCs, and delivery assurance. The low bit error rate and highavailability of the two-way system 100 ensures that packages aredelivered in one transmission (that is, without the need to retransmit).

With respect to ensuring proper delivery and reporting delivery statusof the digital packages, the publisher possesses a number offunctionalities. The PC 101 may issue retransmission requests, asneeded, if segments of the package is loss or received with errors. ThePC 101 may request retransmission of only the loss or corrupt portionsof the digital package via the satellite return channel, or optionally,a dial-out modem It should be noted that the multicasting capability ofthe system 100 advantageously permits the one time retransmission ofmissing/corrupt data even though the missing/corrupt data may affectmultiple PCs. The system 100 also supports delivery confirmation. A PC101, after successfully receiving a package, may send a confirmation toa package delivery server (not shown) within the NOC 113. Theseconfirmations are tabulated and provided in the form of reports to thepublisher.

Further, the system 100 may provide a best effort service. Under thisscenario, if frames are lost on the first transmission, the receivingPCs fill in the gaps on subsequent transmissions. This mechanism helpsensure high probability of delivery without requiring use of a returnlink for retransmission requests.

According to an exemplary embodiment, the digital packages contain thefollowing fields: a transmission rate field that is configurable perpackage at speeds up to 4 Mbps through the IRU; a forward errorcorrection (FEC) rate for providing correction of sporadic packet loss;a priority field for specifying low, medium, or high priority; andoptional topic, descriptive name, and description fields that are usedby the user interface of the receiver PC to present the package to theuser. The package delivery service of the two-system 100 supports thesimultaneous transmission of several packages and the preemption oflower priority packages to ensure the timely delivery of higher prioritypackages.

The system 100 also supplies multimedia services, which provide one-wayIP multicast transport. The NOC 113 relays a configurable set of IPmulticast addresses over the downlink channel. An information providermay pass IP multicast packets to the NOC 113, either via a terrestrialline or via the return channel. The receiving PCs may receive the IPmulticast through the standard Winsock with IP Multicast extensions API.To prevent unauthorized access, each IP multicast address may becryptographically protected. Thus, PC 101 may only have access to anaddress if it has been authorized by the NOC 113. Hardware filtering inthe Indoor Receive Unit (IRU) 109 a allows the reception of any numberof different IP Multicast addresses.

The NOC 113, which provides network management functions, allocates toeach multimedia information provider a committed information rate (CIR),and one or more IP multicast addresses. The CIR specifies the fractionof the broadcast channel bandwidth that is guaranteed to the data feedprovider. Each IP Multicast address operates as a separate data streamthat is multiplexed on the one broadcast channel.

As previously mentioned, the two-way system 100 provides high-speedInternet access, in which the PC 101 can connect to the Internet 105. Inone embodiment of the present invention, the access is asymmetric,whereby the downlink channel from the NOC 113 to the user terminal 101can be an order of magnitude greater that the uplink (or returnchannel).

An NDIS (Network Device Interface Specification) device driver withinthe PC 101 operates with the native TCP/IP stack for Windows. When theITU 109 b is active and enabled, the NDIS software sends the returnchannel data to the IRU 109 a, which in turn supplies the data to theITU 109 b. However, when the ITU 109 b is inactive, the packets may bealternatively sent to a dial-up interface. The two-way system 100 allowsoperation of the standard Internet applications; for example, Netscape®browser, Microsoft® Internet Explorer browser, email, NNTP Usenet News,FTP, GOPHER, etc.

FIG. 3 shows the transceiver components utilized in the system of FIG.1. The transceiver 109 encompasses a number of hardware and softwarecomponents. A PC host software, which is resident in PC 101 and supportsthe satellite return channel. The transceiver 109 includes IRU 109 a,ITU 109 b, a power supply 109 c, and connects to an Outdoor Unit (ODU)307. The ODU 307 contains a low noise block (LNB) 305, antenna 111, anda radio (not shown). The IRU 109 a operates in the receive-only mode andcontrols the ITU 109 b.

As previously indicated, the IRU 109 a may have a Universal Serial Bus(USB) interface, which is a standard interface to PC 101 to provide IRUcontrol and data. The IRU 109 a may be attached to the PC 101dynamically, and may be loaded with operational software and initializedby PC driver software. Received traffic is forwarded to the PC 101through the USB connection 301. The PC driver communicates with the IRU109 a for control over the USB channel. By way of example, the receivechain F-connector on an RG-6 cable is connected to the IRU 109 a tocommunicate to the LNB 305. The IRU 109 a contains an interface that maybe used to transfer data to control the transmit unit and to actuallyprovide the transmit data to the ITU 109 b. A clock is received on thischannel to ensure that transmit frame timing and transmit symbol clocksare synchronized.

The ITU 109 b may be a standalone component that externally may appearvery similar to the IRU 109 a. According to one embodiment of thepresent invention, the housings of the IRU 109 a and ITU 109 b are in astackable form factor. The ITU 109 b has an IFL interface (not shown)that attaches to the ODU 307 via an RG-6 interface (not shown). Controlinformation and data from the ITU 109 b are multiplexed onto the IFLcables 303 to the ODU 307. One IFL cable 303 may handle the receivepatch and the other may handle the transmit path.

The ITU 109 b also includes an ITU control interface for data transfer.In addition, a pulse is received over the ITU control interface toensure that transmit frame timing and transmit symbol clocks areproperly synchronized. The ITU 109 b may contain an RF transmitter, lowphase noise VC-TCXO, and serial data transceiver. ITU 109 b modulatesand transmits, in burst mode, the in-bound carrier at 64 kbps or 128kbps to a Return Channel Equipment (FIG. 4). The ITU 109 b may bedesigned to operate with and to be controlled by the IRU 109 a. AlthoughIRU 109 a and ITU 109 b are shown as distinct components, IRU 109 a andITU 109 b may be integrated, according to an embodiment of the presentinvention. By way of example, a single DB-25 connector on the rear panelprovides power, ground and a serial data link via which control of thetransmitter is exercised. The ITU 109 b may be considered a peripheralto the IRU 109 a. Configuration parameters and inbound data from the IRU109 a may be input to the serial port (not shown); in addition,transmitter status information to the IRU 109 a may output from theserial port.

The IRU 109 a and ITU 109 b utilize dual IFL cables 303 to connect toLNB 305 for receiving signals from the satellite 107. Each cable 303 maycarry the necessary power, data, and control signals from the IRU 109 aand ITU 109 b to the LNB 305, which is mounted on the antenna 111.According to one embodiment, the antenna 111 is a standard 66 cmelliptical antenna, with dimensions of 97 cm×52 cm (yielding an overallsize of approximately 72 cm). Antenna 111 may include mounting equipmentto support an FSS feed, BSS feeds, and a feed bracket.

The transceiver 109 supports a variety of features that enhance theflexibility and efficiency of the two-way system 100. Transceiver 109can be implemented as a receive-only unit that can be later upgraded tosupport a two-way configuration. In other words, the transceiver 109 maybe configured either as a receive-only package or a transmit upgradepackage. The transceiver 109 may be designed to be an add-on capabilityto a standard receive-only transceiver. Thus, in actual implementation,a user can either purchase an upgrade to a transceiver 109 to support asatellite-based return channel or can operate a receiver with notransmit portion for communication over the satellite 107. Such areceive-only system may employ a terrestrial return channel (e.g., phoneline) for two-way IP traffic.

In addition, the transceiver 109 supports multiple rate, high speed,receive channel. The transceiver 109 can support for high speed TCP/IPapplications using, for example, Turbo Internet™ TCP spoofing. In anexemplary embodiment, a standard USB interface to PC 101 is used toconnect the PC 101 with the IRU 109 a; however, it is recognized thatany type of interface can be utilized (e.g., serial, parallel, PCM/CIA,SCSI, etc.). The transceiver 109 supports TCP/IP applications (e.g., webbrowsing, electronic mail and FTP) and multimedia broadcast andmulticast applications using IP Multicast (e.g. MPEG-1 and MPEG-2digital video, digital audio and file broadcast) to PC 101 per the USBadapter connection 301. The transceiver 109 can also support IPmulticast applications (e.g., MPEG video and package delivery). Further,the transceiver 109 can provide compression of receive and returnchannel traffic to enhance bandwidth efficiency.

The transceiver 109 integrates the capabilities of the broadbandreceiver via satellite with the capability for a satellite returnchannel through the use of IRU 109 a and ITU 109 b. The IRU 109 a ispowered by power supply 109 c. As indicated previously, the receivedchannel to the transceiver 109 may be a DVB transport stream thatcontains multiprotocol-encapsulated IP traffic. A group of multipletransmit channels may be shared among several DVB transport streams.

Further, the transceiver 109, unlike conventional satellite systems, iscontrolled at the system level by the NOC 113. Particularly, the NOC 113has the capability to enable and disable the operation of the ITU 109 b,thereby making it difficult for an authorized user to access thesatellite system 100. Neither the transceiver 109 nor the connectedPC-based host 101 has the capability to override commands from NOC 113,even in the case in which the equipment is powered down and restarted.Once disabled, the ITU 109 b can only be enabled by the NOC 113. Thatis, the user cannot “re-enable” a disabled ITU 109 b, even through apower reset. Additionally, the NOC 113 may instruct the ITU 109 b totransmit a test pattern at a pre-determined frequency. This process maynot be overridden by the user, who has no capability to cause thegeneration of the test pattern. The user has no control over thefrequency that the test pattern is sent. Thus, the above system-levelcontrol of the ITU 109 b by the NOC 113 prevents users from utilizingthe resources of the satellite system 100.

FIG. 4 shows the architecture of a network operations center (NOC) inthe system of FIG. 1. A NOC 113 provides various management functions insupport of the return channel from the user terminal 101. Specifically,the NOC 113 provides the high-speed receive channel to the transceiver109 of user terminal 101. The NOC 113 also provides interfaces to eitherprivate Intranets 103 or the public Internet 105, as directed by userterminal 101. The NOC 113 can support multiple receive channels(referred to as outroutes) and multiple return channels; however, theNOC 113 can be configured to provide no return channels, depending onthe application. Further, a single return channel may be shared bymultiple receive channels. Multiple return channels within a single setof Return Channel Equipment (RCE) 411 can operate in conjunction toserve a single receive channel.

Within NOC 113, a Radio Frequency Terminal (RFT) 401 is responsible forretrieving an IF (intermediate frequency) output of a System IFDistribution module 403, up-converting the IF output signal to RF (radiofrequency) for transmission to the satellite 107. Additionally, the RFT401 receives from the satellite 107 an RF echo of the transmittedsignal, along with the RF input for the return channels; the RFT 401down-converts these signals to IF and forwards the down-convertedsignals to the System IF Distribution module 403.

The System IF Distribution module 403 receives as input an output signalfrom outroute modulators 405 via outroute redundancy equipment 407. Inresponse to this input signal, the System IF Distribution module 403sends a signal to the RFT 401 and a Timing Support Equipment module 409.The System IF Distribution module 403 receives an IF output from the RFT401, and distributes the received IF signal to the Timing SupportEquipment module 409 and the Return Channel IF Distribution module 411c.

The modulator 405 encodes and modulates the DVB transport stream from asatellite gateway 413. In an exemplary embodiment, at least twomodulators 405 are used for each uplink for redundancy; i.e., support1-for-1 satellite gateway redundancy. The modulator 405, which may be,for example, a Radyne® 3030DVB modulator or a NewTec® NTC/2080/Zmodulator, is responsible for taking the outroute bit stream receivedfrom the satellite gateway and encoding it and modulating it beforeforwarding it towards the RFT 401.

The satellite gateway 413 multiplexes traffic to be transmitted on theuplink. The multiplexed traffic includes user traffic that is forwardedfrom standard LAN gateways 415 supporting TCP/IP Multicast traffic. Themultiplexed traffic also includes traffic that is forwarded from thereturn channel components 411, which include a Network Control Cluster(NCC) 411 a. The NCC 411 a is a server-class PC running Windows, alongwith DVB satellite gateway software that supports multiple PIDs.

The outroute redundancy component 407 supports a configuration thatallows critical traffic components to fail without causing a systemoutage; this is supported on the IF data following the modulator 405. Ifequipment on one transmit chain fails, the lack of a data signal isdetected and a switch (not shown) automatically switches to anothertransmit chain. In this example, 1-for-1 redundancy of the satellitegateway 413 and modulators 405 is supported.

Within the outroute redundancy component 407, a gateway common equipment(GCE) (not shown) accepts input signals from two modulators 405, inwhich each serves one of two redundant chains for a return channel ofsystem 100. The GCE provides an output interface to the system IFdistribution module 403 for the currently online modulator 405. The GCEalso has a control interface that can be used to switchover themodulator chain. By way of example, the GCE may have a “baseball switch”that can be used for manual switching. In an exemplary embodiment, theGCE may be a standard off-the-shelf GCE component per uplink.Optionally, a DVB GCE may be used if a single modulator 405 is be usedinstead of two per uplink.

The timing support equipment 409 includes multiple gateway up-linkmodules (GUMs) 409 a and 409 b. The GUMs 409 a and 409 b provide atranslation of IF signals to L-band so the signals can be received on areceive-only unit, which controls a GCE switch (not shown) and on atiming unit 409 c. The GUMs 409 a and 409 b receive a signal from theGCE and provides the L-Band signal either directly to a Quality MonitorPC (QMPC) (not shown) or through a splitter (not shown) to multiplereceivers; one of these is connected to the system IF distributionmodule 403 for the uplink signal. The QMPC may be a standardreceive-only version of the transceiver 109 with a relay card thatcontrols the RCU. The QMPC, according to one embodiment of the presentinvention, may include a PC with the Windows operating system. The QMPCcan operate with the IRU 409 d, thereby permitting the IRU 409 d to beused in the QMPC. The IRU 409 d may be able to support more channelsbecause the data is not forwarded to the host and more MAC addresses areused. According to one embodiment, the addressing scheme for messagessupports up to 16 million adapters (i.e., transceivers); extendingbeyond the private class “A” IP address. Accordingly, MAC addressingsupports a greater number of adapters that IP addressing. The high ordernibble of the byte, which is currently set to “0Ah” (10), may be used togive 16 fold improvement to 256 million adapters.

A Redundancy Control Unit (RCU) (not shown) within the outrouteredundancy component 407 controls the GCE switch. The RCU interfaces tothe QMPC, which provides a control channel that triggers the switchingof the GCE. The RCU also includes an interface to the GCE forcontrolling the switch. Further, the RCU has serial interfaces thatinterface to the satellite gateway 413 to indicate which satellitegateway is currently online, thereby ensuring that only the onlinesatellite gateway provides flow control to the gateways.

Several local area networks (LANs) 421 and 423 may be used to connectthe various NOC components together. A Mux LAN 421 is used to multiplextraffic that is to be sent to the satellite gateway 413 for a specificoutroute. A Traffic LAN 423 transports customer traffic that arereceived from the return channel and traffic from the Intranet 103 andInternet 105.

The NOC 113 can maintain several standard gateways 415, 417, and 419that may forward data to the user terminal 101 over LAN 421. Thesegateways 415, 417, and 419 may operate on server-class PCs runningMicrosoft® Windows-NT. A PDMC (Package Delivery and IP Multicast)Gateway 417 forwards package delivery traffic and IP multicast trafficto the satellite gateway 413. The gateway 417 uses key material providedby the conditional access controller (CAC) server 425 to instruct thesatellite gateway 413 whether to encrypt the traffic as well as the keyto be used for encryption.

A Hybrid Gateway (HGW) 419 processes two-way TCP traffic to the users.The HGW 419 provides uplink traffic, handles flow control to respond tosatellite channel overload, and also acts as a proxy for return channeltraffic. For user terminals 101 that generate TCP traffic fortransmission over the return channel, the HGW 419 interacts with thepublic Internet 105 or private Intranet 103 to relay the received usertraffic. The software of the HGW 419 may be modified to support thenetworking functionalities associated with a satellite-based returnchannel. The software supports variable round-trip times in thethroughput limiter calculations; e.g., either a CIR-based or moreintelligent round-trip-time based algorithm may be deployed. TCPSelective acknowledgement may also be supported by the software tominimize retransmission data requirements. Other functionalities of thesoftware include TCP Delayed ACK, larger transmission windows, and HMPoverhead reduction. Further, the software support return channel unitsthat are “always on”. In addition, the software is backwards compatible.

A Dedicated LAN Gateway (LGW) 415 includes the functionality of both thePDMC 417 and HGW 419. The LGW 415 is used for customers that require adedicated amount of bandwidth, in which the customers are permitted toshare the bandwidth among their different applications.

A Conditional Access Controller (CAC) server 425 contains the keymaterial for all of the transceivers 109. According to one embodiment ofthe present invention, uplink traffic is encrypted using keys from thisserver 425. Alternatively, the receive channel may be unencrypted. Thereturn channel traffic could also be encrypted with the transceiver'sindividual key for privacy of data. Multicast traffic is encrypted witha generated key. The CAC server 425 ensures that the key material isprovided to the transceivers 109 that are authorized to receive anybroadcasts. In addition, the server 425 provides the individualtransceiver keys to the gateways 415, 417, and 419. The CAC server 425operates on a server-class PC running Windows NT.

The NOC 113 also contains a Return Channel Equipment module (RCE) 411,which manages the return channels associated with NOC 113. That is, theRCE 411 is responsible for managing return channel bandwidth and forreceiving the return channel traffic from the transceivers 109. The RCE411 may include Network Control Clusters (NCCs) 411 a, one or more BurstChannel Demodulators (BCDs) 411 b, and are responsible for managing thereturn channel bandwidth and the BCDs 411 b. According to an exemplaryembodiment, each RCE 411 has a limit on the number of BCDs 411 b whichan RCE 411 can support. For example, given a 1-for-7 redundancy scheme,up to 28 return channels can be supported. By way of example, multipleRCEs 411 may be deployed to support more than 32 BCDs 411 b worth ofreturn channels. As will be discussed later with respect to FIG. 10,this approach provides a scalable configuration.

The NCC 411 a may be configured to control several RCEs 411. The sitemay be assigned to the NCC 411 a at ranging time. “Ranging” is a processwhich configures a site on a NCC 411 a and adjusts timing of the NCC 411a without user intervention. Sites may periodically either be moved toanother NCC 411 a, which supports a different set of return channels ormay be completely decommissioned from the NOC 113. For instance, a sitemay be moved to another NCC 411 a, as needed, for load balancing. Thesystem 100 is capable of communicating site moves between NCCs 411 a sothe sites are no longer enabled on the prior NCC 411 a. In addition, ade-commission of the site from the CAC server 425 may disable the siteat the NCC 411 a. According to one embodiment of the present invention,the NCC 411 a can access the same database (not shown) as that are usedby the conditional access and auto-commissioning systems.

The RCE 411 further includes Burst Channel Demodulators (BCDs) 411 b,which demodulates return channel transmissions from the transceivers 109and forwards the received packets to the NCC 411 a. Redundancy of the IFsubsystem is supported in the BCDs 411. These BCDs 411 b are one for Nredundant with automatic switchover in the event of a failure. Accordingto an exemplary embodiment, up to 32 BCDs may be supported by a singleNCC 411 a; the RCE 411 may handle up to 32 BCDs (i.e., up to 31 returnchannels).

The RCE 411 also contains a Return Channel IF Distribution module 411 c.The return channel IF Distribution module 411 c receives the IF outputsignal from the System IF Distribution module 403 and forwards theoutput signal to the BCDs 411 b. The sites may be “polled” to ensurethat the BCDs 411 b stay active, thereby proactively detecting failedsites.

As noted above, NCC 411 a is responsible for managing the bandwidth of aset of up to 32 BCDs 411 b. NCC 411 a also provides configuration datato the BCDs 411 b. NCC 411 a also reassembles packets received from thereturn channels (by way of the BCDs 411 b) back into IP packets andforwards the IP packets to the appropriate gateway. The NCC 411 a isinternally 1-for-1 redundant between the two NCCs 411 a by exchangingmessages.

When a frame is received from a receiver, the first byte of data mayindicate the Gateway ID for this serial number. The received frame maybe mapped to an IP address by the NCC 411 a and stored for theparticular individual receiver. Accordingly, other packets can bereceived by this receiver without the 1-byte overhead for the gateway onevery packet. The NCC 411 forwards the packet to the appropriate gatewayafter building an IP-in-IP packet that is compatible with the UDPtunneled packets sent to the gateways.

According to one embodiment, the NCC 411 a may utilize the Microsoft®Windows operating system. The NCC 411 a need not processes or transmitframe timing messages. The NCC 411 a may support changing the format ofoutbound messages to include new MAC addresses as well as differentreturn channel headers. In addition, NCC 113 tracks return channelgateway address to IP mapping; this information is periodically providedto receivers. NCC 411 a may also update and effect BCD configurationfiles, which can be locally stored and managed, without softwarerestart. NCC 411 a can support a large number of transceivers 109 (e.g.,at least 100,000 transceivers).

As indicated previously, the NCC 411 a manages the return channelbandwidth and forwards inbound traffic to the gateways. The NCC 411 amay send a timing pulse to its associated timing units 409 c once every“super frame” before the NCC 411 a pulses the BCDs 411 b to receive theframe. These pulses are provided to the timing units on the returnchannel frame boundary.

NCC 411 a further maintains a transceiver-last-packet-time in a largememory-based sorted array for polling. The polling algorithm poll sitesthat are not recently transmitting or, as needed, to poll known “good”sites to keep BCDs 411 b active. That is, the NCC 411 a performs remotepolling of idle remotes on a periodic basis to keep BCDs 411 b active.The polling message specifies the return channel number to respond on.The remote status assumed to be good if the remote has transmittedpackets. Only the least-recent responders are polled. NCC 411 a candisable transmission from sites with particular serial numbers throughits broadcast.

The Timing Support Equipment (TSE) 409 provides return channel timingsupport for each outroute. TSE 409 may employ a pair of PCs (not shown);each PC runs Microsoft® Windows and are connected to two IRUs 409 d.According to one embodiment of the present invention, a NCC 411 a isallocated to one of the outroutes to ensure a 1-to-1 relationshipbetween NCC 411 a and timing support equipment 409. For each outroutepairing, the TSE 409 may include a pair of Gateway Upconverter Modules(GUMs) 409 a and 409 b, and a timing unit 409 c. The GUMs 409 a and 409b translate the uplink and downlink IF signal to an L-band signal. Theuplink signal is sent to a pair of local timing units 409 c as well asthe outroute redundancy equipment 407. The downlink signal is sent to apair of echo timing units. The timing unit 409 c determines both thevariable satellite gateway delay for the transmit signal and the NOCsatellite delay, and transmits frame timing information to thetransceivers 109.

The timing units 409 c are the portion of the NOC 113 that supportnetwork timing. In an exemplary embodiment, a timing unit 409 c may be aPC with two attached indoor receive units (IRUs) 409 d, both which areconfigured to support timing. When the timing unit 409 c receives thelocal timing, timing unit 409 c may generate a “frame timing” messagewith the prior super frame satellite delay and the current super framedelay. The timing unit 409 c transmits the message to the satellitegateway 413 in an appropriated formatted Traffic Token Ring (TTR)message. Software in the PC may be used to configure the IRUs 409 d inthis mode; a special version of firmware may also be provided to the IRU409 d. One of the IRUs 409 d may provide a time difference from thepulse to the local super frame header, while the other IRU 409 d mayprovide the difference from the pulse to the super frame after the IRU409 d is sent to the satellite 107 and received back at the NOC 113.Further, one IRU 409 d receives the transport stream for the outrouteprior to transmission to the satellite 107. The other IRU 409 d receivesthe transport stream after the transport stream is transmitted to andreceived back from the satellite by way of an L-Band output from thedownlink GUM 409 b.

IRUs 409 a may include hardware to support network timing. The softwareof the timing unit 409 c may use this hardware to perform the necessarytiming unit functions. A timing support task may be included in theembedded software, which operates in the IRU 409 d portion of the TimingUnit 409 c. The host software may receive timing information from thefirmware and may use the information to format frame timing messages.The frame timing messages may be sent to the satellite gateway 413through the MUX LAN 421 using a TTR.

The system 100 also measures and reports usage information on thechannels. This information may be supplied on a periodic basis tobilling, and/or made available on a real-time basis to management nodesin the NOC 113 for troubleshooting and monitoring purposes.

FIG. 5 a shows the system interfaces that are involved with the roundtrip flow of user traffic through the system of FIG. 1. The systeminterfaces permit transceiver 109 to operate without requiringconfiguration information from the host 101. According to one embodimentof the present invention, NOC 113 sends transceiver 109 the necessaryinformation to control and manage the transceiver 109. In this example,user traffic originates from a gateway 419, which is a hybrid gateway,to IRU 109 a. The traffic is sent to the host PC 101, which can initiatetraffic through IRU 109 a, ITU 109 b, and then ODU 307 for transmissionover the return channel The user traffic is received by the NOC 113 viaBCD 411 b. The BCD 411 b forwards the traffic to NCC 411 a to theInternet 105 or Intranet 103 via gateway 419.

The communication among the components 419, 109 a, 101, 109 b, 307, 411b, and 411 a is facilitated by the following interfaces: NOC to IRUInterface 501, IRU to PC Interface 503, IRU to ITU Interface 505, ITU toODU Interface 507, ODU to BCD Interface 509, BCD to NCC Interface 511,and NCC to Gateway Interface 513. The NOC to IRU interface 501 islayered to include DVB, PIDs, and MAC addresses. The IRU to PC Interface503 uses USB super frames to send a large amount of data in a USB burstto the host PC 101. The payloads of the super frames are IP datagramswith the IP header. A new format header may be used for each message toprovide timing and other information to the host PC 101. In the IRU toITU interface 505, the IRU 109 may break the IP datagram into bursts totransmit to the NOC 113. The IRU 109 may send a frame format message foreach frame if there is data to transmit.

The internal NOC interface, IRU to BCD interface, is layered to includethe burst structure, the return channel frame format, and the messagestructure for NCC 411 a messages. The NCC 411 a may forward traffic tothe appropriate gateway 419 (e.g., dedicated gateway or hybrid gateway)in the NOC 113. The data forwarded to the gateway 419 may bere-formatted in a UDP datagram to allow the NOC 113 to receive thetraffic as if it were received over a UDP return channel.

The NOC to IRU interface 501 may utilize a multi-layer protocol, whichincludes the following layers: a DVB transport stream, which can supportmultiple multiprotocol encapsulation messages, for example, in a singleMPEG frame per the implementation and includes fixed-size 204 byte MPEGpackets (which contain 188 bytes of user traffic and 16 bytes of FECdata); a DVB PID, which the receiver may filter traffic based on PIDs;and a DVB MPE, which the receiver may filter traffic based on MACAddress and may process MPE headers for user traffic. The receiver mayalso process service tables for PAT and PMT; data following the MPEheader has been added to support encrypted traffic. The multi-layerprotocol of the NOC to IRU interface 501 may include an IP Payload (thepayload of the MPE is expected to be an IP packet including IP headers)and RCE Messages. It should be noted that specific MAC addresses may beused for return channel messages, which may originate from the NCC 411 aor from a timing unit 409 c.

With respect to the DVB transport stream, the DVB standard multiprotocolencapsulation standard over data piping is employed. The multiprotocolheader includes the following fields used by system 100: a MAC Addressfield (e.g., 6 bytes in length); an encryption field (e.g., a 1 bitfield that can be set if the packet is encrypted); and a

Length field for specifying the length of the packet header. Ifencryption is disabled for the packet, the IP header and payloadimmediately follow the MPE header. If encryption is enabled, then thefirst 8 bytes contain the initialization vector for packet decryption.This vector includes a packet sequence number used to detectout-of-sequence packets. The satellite gateway 413 removes packets fromthe TTR buffers and transmit them on an outroute. The payload andpadding are transmitted following an appropriately formatted MPE headerand the initialization vector (for encrypted packets). The payload ofthe multiprotocol encapsulation frame is determined by the encryptionvalue in the MPE header. If encryption is enabled for the packet, thenthe first 8 bytes contain an initialization key that also acts as thesequence number. If encryption is disabled, the packet is the IPpayload, which is DVB compliant.

As indicated above, the NOC to IRU interface 501 may use DVB compliantMPEG-2 formatting. The header of each frame contains a PID, which isfiltered by the receiver hardware. The receiver is capable of receivingseveral of the PID addresses. The receiver may be configured with thePID addresses it is to use, including the one to be used for its NCC 411c. Each NCC 411 c may be allocated its own private PID to ensure thatreceivers only receive traffic for their allocated NCC 411 c. A TTRbuffer may be used by the gateways, the NCC 411 a, the Local TimingUnit, and the CAC Server to send messages to the satellite gateway fortransmission on the outroute.

As shown in FIG. 5 b, a TTR buffer 521 is carried as the data field of amulticast UDP/IP packet 523, which includes a multicast IP header 525and a UPD header 527. The TTR buffer 521 includes the following fields:a Gateway ID field 529 (8 bits) for specifying the sending gateway ID; aNumber of Packets field 531 (8 bits) for indicating the number ofpackets in this TTR buffer; and a TTR Sequence Number field 533 (16bits) for specifying the sequence number. The TTR Sequence Number field533 is used by the satellite gateway 413 (in conjunction with theGateway ID) to detect TTR buffers lost on the backbone LAN. The TTRSequence Number field 533 is sent least significant byte first; a valueof 0 is always considered to be in sequence. The TTR buffer 521 alsoincludes N packets 535. Within each packet 535 are the following fields:a DES Key field 537, two MAC Address fields 539, a Length field 541, aSequence Number field 543, a Payload field 545, a Padding field 547, andan Alignment field 549. The DES Key field 537, which is 8 bytes inlength, specifies the encryption key to be used by the satellite gateway413 to encrypt the packet 523. When no encryption is required (e.g., forNCC 411 a packets), zero is placed in this field 537. Two copies of theMAC Addresses (each have a 6-byte length) are stored in field 539. Thefirst copy is the spacelink MAC address placed in the DVB Header. Thesecond copy of MAC Address is supplied for backward compatibility. TheLength field 541 (2 bytes) indicates the length of the packet 535 (leastsignificant byte first). The Sequence Number field 543 indicates thepacket number of this Next TTR frame. In an exemplary embodiment, thePayload field 545 has a variable length from 1 to 8209 bytes and storesthe message that is to be sent on the outroute (e.g., an IP packet). Thelength of the Payload field 545 may be limited to the maximum Ethernetframe size, for example. The Padding field 547, which may vary from 0 to3 bytes, makes the packet 535 a multiple of long words when transmittedon the outroute; this is required for proper DES encryption. TheAlignment field 549 is a 2 byte field and provides filler betweenpackets, ensuring that the next packet starts on a 4 byte boundary. ThePadding field 547, in an embodiment of the present invention, leaves thepacket 535 2 bytes short of the proper boundary to optimize satellitegateway 413 processing of the TTR buffer 521.

The total size of a TTR buffer is only limited by the maximum data fieldsize of the UDP packet 523. Typically, a maximum UDP packet size of 8192or 16234 is used on the backbone LAN. Gateways need to forward data athigh speed and typically send large TTR buffers with multiple IP packetsin them. The CAC Server 425 does not need to send at high speed but doessend multiple packets in TTR buffers for efficiency. NCCs 411 a and theLocal Timing Unit send messages at a much lower rate than the IPGateways and typically may only send one message in each TTR buffer inorder to reduce latency and jitter.

Each sender of outroute messages in the NOC 113 may be assigned a uniqueGateway ID for each of the traffic streams it may forward to thesatellite gateway 413. The NCC 411 a, Local Timing Unit 409 c, and theCAC Server 425 are each assigned a single Gateway ID. Gateways handlingunicast traffic may be assigned two Gateway IDs for their unicasttraffic to support prioritization of interactive traffic ahead of bulktransfers.

The satellite gateway 413 may use the Gateway ID to map an incoming TTRbuffer 521 to the correct priority input queue. satellite gateway 413can support up to 256 senders. The NCC 411 a, Local Timing Unit 409 c,and CAC Server 425 traffic should be prioritized ahead of all usertraffic. This is necessary to ensure minimal propagation delays and alsobecause these traffic types have very low throughput. The NCC 411 ashould be prioritized ahead of all other traffic to ensure that thesuper frame header is transmitted as soon as possible to ensure that thereturn channel timing is received in time at the transceivers.

The following types of addresses may be used within a Return Channel ofsystem 100: Ethernet MAC addresses; IP unicast addresses; and IPmulticast addresses. For most IP based communication, UDP is used on topof IP. All references to communication using IP (unicast or multicast)addresses, also imply the use of an appropriate (configurable) UDP portnumber. In some cases, for example, the conditional access IP multicastaddress and the flow control IP multicast address, the same specific IPaddress may be used with different UDP port numbers.

Each LAN port in the NOC 113 has an Ethernet MAC address assigned to it.The Ethernet MAC address of a LAN port is simply the burned in IEEE MACaddress of the NIC (Network Interface Card) that is used to implementthe LAN port. The PC may also use Ethernet MAC addressing if a NIC isattached to the PC for forwarding traffic onto a LAN.

System 100 also makes use of multicast Ethernet MAC addresses forcarrying multicast IP traffic and the broadcast Ethernet MAC address forcarrying broadcast IP traffic. All communication at the NOC 113 (andmost of the communication within system 100 in general) is IP based.Every NOC component has (at least) one IP unicast address for each ofits LAN ports. These addresses are local to the subnet to which the LANport is attached.

Specific receivers are assigned an IP Unicast address that may be usedfor all unicast traffic to and from the transceiver. This address isallocated to the site at auto-commissioning time and is bound to the TCPprotocol for the USB adapter on the user equipment. At the same time, aspecific gateway is configured with the serial number/IP address mappingfor that transceiver. These unicast addresses may be private addressessince the interface to the internet in both directions may be throughNOC equipment that can translate to a public IP address.

In addition to its Satellite Card IP unicast addresses, Transceiver 109uses a private class-A IP address based on the serial number for its CACindividual traffic. IP multicast addresses are used (for efficiency) forall communication on the MUX LAN 421 where there are potentiallymultiple receivers, including cases where the multiple receivers onlyexist because of redundancy. There are at least four types of IPmulticast addresses used in system 100: (1) the satellite gateway IPmulticast address; (2) conditional access IP multicast addresses; (3)the flow control IP multicast address; and (4) User traffic IP Multicastaddresses. The first three address types are private to the MUX LAN 421;the fourth address type is public and used for the traffic LAN 423.

The addresses may be selected by the hub operator and configured intothe appropriate components. The satellite gateway IP multicast addressis used to forward messages to the satellite gateway 413 to betransmitted onto the outroute. All of the senders of traffic (theGateways, the NCC 411A, the CAC, and the Local Timing Unit) send to thissame address. Messages are sent to the satellite gateway 413 in TTRbuffers. TTR buffers are UDP/IP multicast packets with a specific formatfor the UDP data field. satellite gateway handling of TTR buffers, aspreviously described.

A conditional access IP multicast address may be used by the CAC Server425 to send conditional access messages to all of the gateways. Twoconditional access IP multicast addresses may be used: one for sendingkey information for unicast traffic, and one for sending key informationfor multicast traffic. Separate addresses may be defined for thispurpose to minimize key handling load on gateways that do not need toprocess a large number of individual keys.

The flow control IP multicast address is used by the satellite gateway413 to send flow control messages to all of the Gateways. The NCC 411 amay be configured with the IP Multicast addresses it is allowed toforward to the traffic LAN. Each gateway may be configured with the setof IP multicast addresses that it may forward to the outroute. Ifmessages appear on the Traffic LAN which match an address in thegateway, the gateway formats the data into TTR buffers and uses the keyprovided by the CAC server 425 for the multicast address.

System messages are messages generated and used internally by the NOCsubsystem. The system messages include conditional access messages, flowcontrol messages; and redundancy messages. All message formats definedby the return channel may be little endian. Existing messages which arereused for the return channel may retain the big or little endianorientation they currently have.

Conditional access messages may be sent by the CAC Server 425 to deliverconditional access information, e.g. keys. There are at least two typesof conditional access messages: gateway conditional access messages, andtransceiver conditional access messages. Conditional access messages maybe unidirectional. That is, messages are only sent from the CAC Server425, not to the CAC Server 425.

The CAC Server 425 sends encryption keys to the gateways. All of theunicast encryption keys for every enabled serial number are sent to allof the gateways. The gateways may store the received keys in a table.The CAC Server 425 also sends encryption keys to the gateways formulticast service elements. The gateways may store the received keys ina table and use the table to extract multicast encryption keys forforwarding multicast IP packets. The CAC Server 425 sends encryptionkeys, using the backbone LAN, to the conditional access IP multicastaddresses. The rate at which these conditional access messages are sentis controlled by parameters in the CAC Server 425. The messages are sentto support relatively quick notification in the event of a key changeand/or the addition of a new transceiver and to support new andrestarted Gateways.

The CAC Server 425 sends decryption keys to the transceivers 109.Unicast keys may be sent in Periodic Adapter Conditional Access Update(PACAU) messages, addressed to the specific transceiver's unicastconditional access spacelink MAC address. The PACAUs also may containmulticast keys for the multicast service elements for which thetransceiver 109 has been enabled. The mapping of service elements toactual multicast addresses may be sent by the CAC Server 425 in Periodic(Data Feed) Element Broadcast (PEB) messages. These messages may be sentto the broadcast conditional access spacelink MAC address. All of thetransceivers 109 receive the PEB messages. The transceiver 109 alsosupports the reception of the extended PEB format, which allows avirtually unlimited number of IP multicast addresses by providing thecapability to segment the PEB.

Flow control messages may be sent by the satellite gateway 413 to theaccess gateways. The satellite gateway 413 measures the average queuelatency in the satellite gateway 413 for each of the priority queues.This information may then be sent to the gateways, mapped to the gatewayIDs. The gateways may use this information to increase and decrease theamount of TCP spoofed traffic being accepted and forwarded from IP hostsat the hub. Flow control messages are unidirectional, i.e. they are onlysent from the satellite gateway 413 toward the IP gateways.

Outbound multicast user traffic, (e.g. file broadcast or MPEG-2 video),is received by an access gateway. The access gateway may be configuredwith the list of IP multicast addresses that it should forward andreceives encryption keys for these IP multicast addresses from the CACServer 425. If the gateway receives an IP packet with a multicastaddress that has not been enabled, the packet is discarded. The IPgateway forwards an IP packet for a multicast address that has beenenabled, along with the appropriate spacelink MAC address and encryptionkey, as a packet payload in a TTR buffer. The satellite gateway 413 mayextract the IP packet from the TTR buffer, encrypts it and forwards itto the outroute.

An application on the PC 101 opens an IP multicast when it wants toreceive the Outbound Multicast stream. The driver may calculate theappropriate MAC address and configures the IRU 109 a to receive trafficon the MAC address. The PC driver may forward IP packets based on themulticast address to the applications that have opened the address.

IP Multicast traffic need not be sourced over the return channel. Whereinroute bandwidth can be allocated to users, it could be sourced overthe return channel by enabling the transceiver 109 to send IP Multicastper the service plan of the transceiver 109. TCP traffic may be spoofedat the NOC 113 to allow for higher speed throughputs even with satellitedelay. The Access gateway software may buffer additional traffic fortransmission through the satellite and locally acknowledge Internettraffic.

Base upon the user service plan selections, connections may be initiatedthrough the Internet 105 to a specific transceiver 109 by using the IPaddress associated with the transceiver. If the transceiver 109 is usingNetwork Address Translation (NAT) to the Internet 105,Internet-initiated connections may not be possible since the publicInternet address is not associated with a specific private addressassociated with the transceiver until a connection is initiated fromwithin the NOC 113.

The TCP User traffic, when initiated at the PC 101, may be passedthrough the system 101 as follows. PC 101 sends an IP Packet to IRU 109a; in turn, the IRU 109 a transmits IP packets (possibly in multiplebursts) to the NOC 113. The NCC 411 a reassembles and forwards the IPpacket to the gateway. The gateway communicates with the destinationhost and receives the response. The gateway sends the IP packets to theIRU 109 a. A NCC 411 A may receive return channel packets from thereturn channels. Each packet may be a subset or a complete IP packet.When the packet is a partial IP packet, the complete IP packet may bereassembled prior to passing the IP packet to an access gateway. Firstand last bits and a sequence number may be used in each return channelframe to provide the necessary information for the NCC 411 a to rebuildthe message. The NCC 411 a may be able to rebuild packets from manytransceivers at once. In addition, multiple data streams may besupported from the same transceiver to support prioritization oftraffic.

Within the system 100, packets are formatted using multiprotocolencapsulation. Therefore, all packets include a DVB-standard header thatincludes a MAC address. For different types of traffic, the MAC addressis set differently. The following types of MAC addresses exist: Unicasttraffic; Multicast traffic; Unicast conditional access; Multicastconditional access; Return Channel Broadcast messages; and ReturnChannel Group messages.

Table 1, below, lists exemplary MAC addresses, according to anembodiment of the present invention.

TABLE 1 Field Size Scope Description Serial Number 24 Bits UnicastSerial number burned into the IRU IP Multicast Address 20 Bits MulticastIP Multicast addresses are 32 bit addresses with format a.b.c.d, whereoctet “a” may be 224-239. Type Indicator 2 Bits All Indicates type ofaddress: 1 - Multicast 2 - Unicast 3 - Internal multicast

Table 2, below, lists the MAC addresses associated with the varioustraffic types that are supported by the system 100.

TABLE 2 Address Type Value MAC Address (Hex) Unicast User Traffic SerialNumber 1 02 00 0A 00 00 01 Serial Number 2 02 00 0A 00 00 02 SerialNumber 256 02 00 0A 00 01 00 IP Multicast Traffic 225.2.3.4 01 00 6E 5203 04 239.221.204.1 01 00 6E 5D CC 01 Unicast Cond. Access Serial Number1 02 00 0A 00 00 01 Serial Number 2 02 00 0A 00 00 02 Serial Number 25602 00 0A 00 01 00 Multicast Cond. Access Broadcast 03 00 00 00 00 00Return Channel Messages Broadcast 03 00 00 00 00 01 RC Group MessagesBroadcast-RCE1 03 00 01 00 00 01 Broadcast-RCE2 03 00 01 00 00 02

A unicast traffic MAC address may be used for traffic that is sent overthe outroute to a specific receiver. The MAC address is determined bythe serial number of the IRU 109 a; the same MAC address is also usedfor CAC individual traffic. The IP Multicast address is determined fromthe IP multicast address using the TCP standard. This standard only mapsthe last two octets of the IP address and part of the second octet ofthe IP address. Therefore, addresses should be configured to ensure thatmultiple IP addresses that map to the same MAC address are not used.

The transceiver 109 periodically receives a list of keys for multicasttraffic. If the transceiver 109 is enabled to receive the multicastaddress, then the IRU 109 a may enable reception of the appropriate MACaddress when an application uses standard Winsock calls to receive froman IP multicast address. Part of enabling the address may be theretrieval of the relevant encryption key and passing that key to the IRU109 a.

The Unicast Conditional Access MAC address is used by the CAC Server 425to send unicast conditional access messages to a specific transceiver.The address is the same as its unicast traffic MAC. Information about asite's access to different multicast streams and whether it is enabledare periodically transmitted to a site over this address.

The Multicast Conditional Access is used by the CAC Server 425 tobroadcast global conditional access information to all transceivers 109.The list of multicast addresses and their keys are periodically providedto all receivers 109. These messages are transmitted unencrypted.

The Return Channel Messages address is used for messages that may bereceived by all adapters 109 on specific transponders, including thosemessages required for the commissioning process. Theses messagesreceived on this address are processed directly in the IRU 109 a, so theIP header is not used at the receiver and should be ignored. The IPdatagram includes the following packet types: a Super-frame NumberingPacket (SFNP), which provides a timing reference and identification forthe transponder; and an Inroute Group Definition Packet (IFDP), whichdefines available return channel groups and resources available on eachgroup.

The Return Channel Group Messages address is used for messages sent on aspecific return channel group to transceivers 109, which are assigned tothe particular group. The grouping is implemented to provide a scalableapproach to transmitting information so that a single site does not needto process 300 return channels. The messages received in this addressare processed by the IRU 109 a, so the IP header is not used by thereceiver and should be ignored. The IP datagram may include thefollowing packet types: Bandwidth Allocation Packet (BAP), InrouteAcknowledgement Packet (IAP), and Inroute Command/Ack Packet (ICAP). TheBAP contains the bandwidth allocation structure and the allocation ofthe bursts to each site on the group. The IAP contains a list of thebursts for a specific frame and a bitmask indicating if the frame wassuccessfully received at the NOC 113. The ICAP contains a list ofcommands to be sent to IRUs 109 a from the NCC 411 a.

Exemplary packets are sent for local processing in the IRU 109 a tosupport the Return channel. Because these packets can be identifiedbased on the MAC address, they need not be encrypted; consequently,these MAC Addresses can be dynamically added and removed by the IRU 109a. All of these packets that are intended to be processed from the IRU109 a may have UDP/IP headers on them, but these headers may be ignoredand assumed to be correct from the IRU 109 a; an exception is that sincethere may be padding on the Outroute for word alignment, the length ofthese packets may be taken from the UDP Header.

To ensure these messages are processed in the proper order within theIRU 109 a, these messages may all be transmitted on the same PID. Itshould be noted that no assumption is made about the order of messagesthat are sent from different NCCs 411 a, largely because of the possibleNOC side network delays.

All the fields in the return channel packets may be encoded using a BigEndian (Network Byte Order) format. Specifically, the structure of thebits for these packets may start with bit 7 of byte 0, and afterreaching bit 0 in each byte, they may wrap into bit 7 of the next byte.When a field has bits crossing over the byte boundary, the lowernumbered bytes may have the higher place value. For example if a 13 bitfield started on bit 2 of byte 7, then the 3 most significant bits(12:10) would come from byte 7 bits 2:0, the 8 next most significantbits (9:2) would come from byte 8, and the 2 least significant bits(1:0) would come from byte 9 bits 7:6.

According to an embodiment of the present invention, the bandwidthassociated with these packets is 700 Kbps, of which only 225 Kbps may beprocessed by a given IRU 109 a. This is equivalent to just under 168MPEG packets per super frame, although the total usable bandwidth maydepend on the NPEG Packet packing. This bandwidth may require for eachoutroute. Although the SFNP may have to be distinct for each outroute,the other packets can be identical for all outroutes that share thecommon Return channels. All of these frames may be sent with very highpriority by the appropriate satellite gateway and the Super FrameNumbering Packets may require the highest priority in the system.Encoding of these packets is especially crucial, as incorrectinformation, and malformed packets can cause IRU misoperation, includingtransmitting on incorrect frequencies. These messages may all be UDPdatagrams, which may include the following packet types: superframenumbering packet (SFNP), Inroute Group Definition Packet (IGDP),Bandwidth Allocation Packet (BAP), Inroute Acknowledgement Packet (IAP),and Inroute Command/Acknowledgement Packet (ICAP). The structures ofthese packets are discussed below with respect to FIGS. 6A-6O.

FIGS. 6A-6O are diagrams of the structures of exemplary packets used inthe system of FIG. 1. The SFNP packet is used to lock network timing forthe return channels and as a beacon to identify the proper network. Asuper frame numbering packet (SFNP) 601, as seen in FIG. 6A, includes an8-bit frame type field 601 a, which has a value of 1 to specify that thepacket 601 is a SFNP. A Timing Source field 601 b has a length of 1 bitand is used to distinguish the particular timing unit that generated theSFNP. This field 601 b may be used to resolve confusion duringswitchover between redundant timing references in the NOC 113. A 7-bitVersion field 601 c is used to indicate the return channel protocolversion. If an adapter 109 does not recognize a protocol version asspecified in this field 601 c, then the adapter 109 does not transmit oruse any of the incoming packets that are related to the return channels.According to one embodiment of the present invention, this protocol mayonly append additional information onto the packet 601, without changesto these existing fields. In this manner, a beacon function for dishpointing can be maintained, irrespective of version.

The SFNP 601 includes a Frame Number field 601 d, which is 16 bits inlength and is incremented by 8 each super frame, and is used to identifyglobal timing; the Frame Number field 601 d may wrap every 49 minutes. A32-bit Local Delay field 601 e captures elapsed time, as obtained from atiming unit, between a previous super frame pulse and the reception ofthe SFNP through the local equipment. The value of 0 for this field 601e may be used to indicate that the value is unknown for the super frame.The IRU 109 a may need to receive 2 consecutive SFNP to be able tointerpret this field 601 e. Additionally, a 32-bit Echo Delay field 601f indicates the elapsed time between two prior super frame pulses andthe reception of the SFNP 601 through the satellite 107. As with theLocal Delay field 601 e, the value of 0 indicates that the value isunknown for the super frame. The IRU 109 a may need to receive threeconsecutive SFNP 601 to be able to interpret this field 601 f. A SFNPInterval field 601 g, which is 32 bits in length, specifies the elapsedtime between the current super frame pulse and a previous frame pulse.This may allow the IRU 109 a to adjust for any differences between thelocal measurement clock (nominal 8.192 MHz), and the clock used by thetiming units, which may be different. The value of 0 may be used toindicate that the value is unknown for the previous super frame. Becauseof the high accuracy of the timing units, the IRU 109 a may only need toreceive three consecutive SFNPs 601 to interpret this field 601 g. ASpace Timing Offset field 601 h is a 32 bit field that specifies atiming offset value. A Reserved field 601 i, which is 2 bits in length,has a 0 value when transmitted; this field 601 i can provide a mechanismto confirm whether the correct satellite network is being monitored.Further, a 15-bit Frequency field 601 j specifies the frequency of theoutroute satellite transponder, in units of 100 kHz. A Longitude field601 k, which is 15 bits long, indicates the longitude of the OutrouteSatellite, in which bit 14 is the West/East_indicator, bits 13:6 are thedegrees, and bits 5:0 are the minutes.

The SFNP uses 1 packet per Super Frame, or 2 Kbps of bandwidth, and istransmitted on the beacon multicast address. The processing of thesepackets are as follows. If the FLL (frequency lock loop) Lock is lost,then no timing can be derived from the SFNP, and network timing isdeclared as out of Sync. Both timing source may be monitored, ifpresent, but a change in selection may only be made after receiving 3consecutive SFNP from the same source when no network timing source isselected. In addition, network timing is declared as in Sync, only afterreceiving 3 consecutive SFNP from the selected timing source, and havingthe local timing match within a given number of clocks. This maytypically require 4 super frame times. Network timing is declared as outof Sync, after receiving 2 consecutive SFNP from the selected timingsource, and having the local timing being off by more than a givennumber of clocks. Additionally, network timing is declared as out ofSync, and the network timing source becomes unselected, after not havingreceived any SFNP for 3 super frame times. Further, network timing isdeclared as out of Sync, and the network timing source becomesunselected, after not receiving 2 consecutive SFNP for a given number ofsuper frame times. In addition, network timing is declared as out ofSync, and the network timing source becomes unselected, after notreceiving 3 consecutive SFNP for a given number of super frame times.

The Inroute Group Definition Packet (IGDP) packet may be used to definethe Return channels on a return channel group, and to allow selection ofreturn channel groups for Aloha and Non-allocated ranging. Returnchannel groups are used to allow for load sharing between a number ofreturn channels, and to minimize the outroute bandwidth required tocontrol the return channel bandwidth allocation. They also may limit theamount of information that needs to be cached or processed by the IRU109 a.

As seen in FIG. 6 b, an inroute group definition packet 603 includes thefollowing fields: a Frame Type field 603 a, an Inroute Group ID(identification) 603 b, a Reserved field 603 c, a Return Channel Typefield 603 d, an Aloha Metric field 603, a Ranging Metric field 603 f,and a Frequency Table field 603 g. For the inroute group definitionpacket 603, the 8-bit Frame Type field 603 a has a value of 2. TheInroute Group ID field 7 is 7 bits long and identifies a particularinroute group. The 13-bit Reserved field 603 c has a 0 value and isignored during reception. The Return Channel Type field 603 d use 4 bitsto indicate the type of return channels that are defined in the inroutegroup; e.g., the value of 0 is defined as 64 Kbps with convolutionalencoding. The Aloha Metric field 603 (a 16 bit field) is used for randomweighted selection of a return channel group when going active, and isbased on the number of Aloha bursts that are defined and the collisionrate on those bursts. The metric value also accounts for loading on theNCC 411A, or the Return channel Group. For example, a value of 0indicates that Aloha is not currently available on this Return channelGroup. The Ranging Metric field 603 f, which is 16-bits, is used forrandom weighted selection of a Return channel Group when performingNonallocated Ranging. The ranging metric value is based on the number ofNonallocated Ranging bursts that are defined and associated collisionrate on those bursts. For example, a value of 0 indicates thatNonallocated Ranging is not currently available on this Return channelGroup. Lastly, the packet 603 has a variable length (N×24 bits)Frequency Table field 603 g, which is used to transmit on each of thereturn channels in the group. Changing the Frequency for a returnchannel must be carefully coordinated to avoid interruptions of networkoperation, or transmission on the wrong return channel frequency aroundthe switch over point. According to one embodiment, there is an upperbound of no more than 4K return channels between all return channelgroups for an outroute. The upper bound for the number of returnchannels in each return channel group depends on the limit of the numberof Burst Allocations in the Bandwidth Allocation Packet (FIG. 6 c). Thevalue of N is derived from the length of the IP Datagram; this uses 1packet per Return channel Group per Super Frame, or 26 Kbps of bandwidthfor 75 Return channels per Group, and 300 return channels. The packet603 is transmitted on the all IRU Multicast address.

Each IRU 109 a may be expected to monitor all Inroute Group DefinitionPackets The IRU 109 a filters out Return channel Types that the IRU 109a is not configured to support, and age out the definition if notreceived for 3 Super Frame times. The table that is created in each IRU109 a from all of these packets should be almost static, with theexception of the Metrics This is to minimize the overhead in the IRU 109a for reorganizing the Inroute Group Table, and because these changesmay disrupt network operation.

When an IRU 109 a is active, the IRU 109 a may monitor its currentInroute Group, as well as a second Inroute Group around the time the IRU109 a is moved among Inroute Groups. To limit latency when an adapterneeds to go active, all inactive adapters with valid Ranging informationmay use the following procedures. Every 4th frame time in the SuperFrame, the IRU 109 a may make a random weighted selection between allthe Inroute Group's that advertise a non-zero Aloha Metric, and maystart to monitor that Inroute Group. The previous Inroute Group may needto be monitored until all previous Bandwidth Allocation Packets havebeen received, or lost.

For every frame time, the IRU 109 a may randomly select one of the Alohabursts from the Bandwidth Allocation Packet for the Inroute Group thatis selected for that frame time. When the IRU 109 a goes active and hasno outstanding Aloha packets, the IRU 109 a may select a random numberof frames (from 1 to 8), ignoring any frame times that had no Bandwidthavailable, it may transmit a single burst during the randomly selectedframe time, and wait to be acknowledged. If the IRU 109 a has notreceived an acknowledgement (e.g., the acknowledgement is lost), the IRU109 a may resend the Aloha packet. After a number of retries indicatedin the SFNP, the adapter should classify the ITU 109 b asnon-functional, and wait for user intervention. While the Aloha packetis outstanding, the IRU 109 a may monitor up to 3 Inroute Groups: (1)one for the Aloha Acknowledgement, (2) one for the new Inroute Group totry, and (3) one for the previous Inroute Group.

In order to limit latency when an adapter needs to go active, allinactive adapters with invalid Ranging info may use a similar procedurefor Nonallocated Ranging bursts. The approach may be augmented toinclude a default Power Level for the first Nonallocated Ranging burst.Further, this power level may be increased until the RangingAcknowledgement is received by the IRU 109 a.

A bandwidth allocation packet (BAP), shown in FIG. 6C, is used to definethe current bandwidth allocation for all inroutes connected to anInroute Group. The packet 605 includes an 8-bit Frame Type field 605 a(which has a value of 3 to indicate a BAP), and a 16-bit Frame Numberfield 605 b, which indicates the Frame Number that is allocated in thispacket 605, and may be larger than the current Frame Number. Thedifference between the frame numbers is a fixed offset to allow the IRU109 a sufficient time to respond to changes in bandwidth allocation. ABurst Allocation field 605 c has a length of N×24 bits and specifies allthe burst allocations for each Inroute. The field 605 c may order allthe bursts in a Frame, and may repeat a Frame for each Inroute in theGroup; the field 605 c is limited to no more than 489 entries, since IPDatagrams are limited to 1500 bytes. This feature enables the IRU 109 ato perform a linear search. An incorrect Burst Allocation Table cancause improper operation of the network, as there is limited errorchecking on this field 605 c. The value of N is derived from the lengthof the IP Datagram.

FIG. 6 c shows an exemplary burst allocation field of the packet 605 inFIG. 6C. The Burst Allocation field 607 includes an Assign ID field 607a, a Ranging field 607 b, a Reserved field 607 c, and a Burst Size field609 d. The Assign ID field 607 a provides a unique identifier that isused to indicate the particular Adapter that has been allocated thebandwidth. A value of 0 for the field 607 a indicates Aloha (andNonallocated Ranging) bursts; the value of 0xFFFF may be used toindicate unassigned bandwidth. Other values are dynamically assigned.The NCC 411 A may impose other reserved values, or structure on thesevalues, but the Adapter may only know what is explicitly assigned to itand 0. The Ranging field 607 b specifies whether the burst is allocatedfor normal or ranging bursts. Even though an adapter may be designatedas ranging, that adapter may be able to send Encapsulated Datagrams overthe Inroute; and an active user may have Ranging turned on/off to testor fine tune it's values, with minimal impact on performance. TheReserved field 607 c should have a value of 0 upon transmission andignored on reception. The Burst Size field 607 d is in terms of slotsand includes the aperture and burst overhead.

For each Frame, the IRU 109 a may receive another Bandwidth AllocationPacket from the Inroute Group it is currently expecting to receivebandwidth allocation on. The IRU 109 a may need to scan the entire tableto obtain the necessary information to transmit data, and processacknowledgements. In an exemplary embodiment, the Burst Allocation field605 c may contain the following fields: Inroute Group, Inroute Index,Frame Number, BurstID, Burst Offset, Burst Size, and AcknowledgementOffset. Since the IRU 109 a can be monitoring two Inroute Groups, theIRU 109 a may need to confirm the Inroute Group based on the MAC Addressof the packet 605, and only process the Bandwidth Allocation Packet 605for which IRU 109 a expects to use bandwidth. The Inroute Index is theCumulative Burst Offset DIV Slot Size of a frame, and is used as anindex into the Frequency Table field 603 g of the Inroute GroupDefinition Packet 603. Frame Number within the Bandwidth Allocationfield 605 c can come from the Frame Number field 605 b of the packet603. A BurstId field may be the 4 least significant bits of the Indexinto the Burst Allocation field 605 c. The Cumulative Burst Offsetstarts at 0, and increases with the each Burst Size. The Burst Offset iseffectively the Cumulative Burst Offset MOD Slot Size of a Frame. TheBurst Size may come from the Burst Allocation packet (FIG. 6D). AnAcknowledgement Offset field is an Index into the Burst Allocation Tableof the entry.

This uses 1 packet per Inroute Group per Frame, or 535 Kbps of bandwidthfor 25 active users per inroute, 75 Inroutes per Group, and 300inroutes. Since it is transmitted on the Inroute Group's Multicastaddress, each IRU may only have to process 134 Kbps.

To ensure that active users do not experience degraded performance ordata lost by any load balancing at the NCC 411 a, at least ten framesprior to moving an IRU 109 a to a different Inroute Group (but on thesame NCC 411 a), the IRU 109 a may be notified, so that it can begin tomonitor both Inroute Group streams. This feature permits the system 100to scale. The IRU 109 a may need to continue monitoring both streams,until all outstanding Inroute Acknowledgement packets are received, orhave been identified as lost. There may be at least 1 frame time with nobandwidth allocated between bursts that are allocated on differentInroutes; this ensures that the IRU 109 a may be able to fill all itsassigned slots, and have at least 1 frame time for tuning. The aboverequirement may apply to bursts that are defined across consecutiveBandwidth Allocation Packets, and when moving between Inroute Groups onthe same NCC 411 a. However, if this requirement is not met, to avoidtransmission across multiple frequencies, then transmission may bedisabled during one of the assigned frames, rather than permittingtuning during a transmission. There may be at least 1 complete framewith no bandwidth allocated between normal and Ranging bursts, therebyensuring that the IRU 109 a may be able to fill all it's assigned slots,and yet have at least 1 frame time for tuning and adjusting transmissionparameters. After the Bandwidth Allocation packet (which moves an IRU109 a to a different Inroute Group) is sent, the NCC 411 a may continueto receive bursts under the old Inroute Group for a time in excess ofthe Round Trip Delay. The NCC 411 a should be prepared to accept theseframes, and to acknowledge them, and the IRU should continue to monitorthe Acknowledgements from the old Inroute Group. An IRU 109 a may nothave its bandwidth moved to a different Inroute Group, while the IRU 109a is still monitoring a previous Inroute Group the IRU 109 a has justbeen moved from—i.e., the IRU 109 a need only monitor up to 2 InrouteGroups.

An adapter may only be assigned multiple bursts during a single frametime under three conditions. First, if these bursts are all on the sameInroute. Second, the bursts are adjacent to each other (i.e., back toback) in the frame. The adapter may transmit one packet for eachallocated burst, but without the Burst Overhead of turning the Radio onand off for each packet. In the third case, all of the bursts, exceptthe last, may be large enough for the maximum sized packet (largestmultiple of the slot size≦256), but only the first burst may have theBurst Overhead/Aperture included in its size. Accordingly, the system100 is constrained to no more than 6 bursts per frame to support 256Kbps Inroutes.

Once an AssignID is assigned to an adapter on an Inroute Group, theassignment may not change while the adapter remains active—except aspart of a move between Inroute Groups. Once an AssignID is assigned toan adapter on an Inroute Group, it may be left unused for five superframe periods after it is no longer in use.

It is important to note that if an Inroute Group advertises that it hasAloha or Nonallocated Ranging bursts, than it may have some number ofthose bursts defined every frame time—e.g., for the next ten frametimes. Furthermore, the number of bursts should be evenly spread acrossall frames in the Super Frame. Failure to meet this requirement mayresult in higher collision rates, and increased user latency.

The IAP packet is used to acknowledge each Inroute packet for assignedbandwidth with a good CRC, regardless of the presence of anyencapsulation data. Besides allowing for faster recovery to inroutepacket errors, this may also allow measurement of the inroute PER at theIRU. Aloha and Nonallocated Ranging packets are acknowledged explicitly.

FIG. 6 e shows the structure of an inroute acknowledgement packet,according to an embodiment of the present invention. An inrouteacknowledgement packet contains the following fields: a Frame Type field609 a, a Frame Number field 609 b, and an ACK field 609 c. For this typeof packet, the Frame Type field 609 a is given a value of 4. The FrameNumber field 609 b specifies the Frame that the acknowledgement applies,which may be less than the current Frame Number. The ACK field 609 c isa bitmap, that matches the entries for this Frame in the BurstAllocation field 605 c of the Bandwidth Allocation Packet 605. Todetermine what was acknowledged, the IRU 109 a may determine whichbursts were assigned to it by the Bandwidth Allocation Packet 605,recalling the data that was transmitted during those bursts. The valueof N is derived from the length of the IP Datagram, and may match thevalue of N from the associated Bandwidth Allocation Packet 605.

This uses 1 packet per Inroute Group per Frame, or 57 Kbps of bandwidthfor 25 Active Users per Inroute, 75 Inroutes per Group, and 300inroutes. Since it is transmitted on the Inroute Group's Multicastaddress, each IRU may only have to process 15 Kbps.

FIG. 6 f shows the structure of an inroute command/acknowledgementpacket, according to an embodiment of the present invention. An inroutecommand/acknowledgement packet 611 is used to explicitly acknowledgeAloha and Nonallocated Ranging bursts, and to send commands to anAdapter. Acknowledgment packets are sent on the Inroute Group'sMulticast address, and commands are sent on the All IRU Multicastaddress. These packets are multicast to reduce Outroute bandwidth, andsince there is no IRU unicast address. The inroutecommand/acknowledgement packet 611 includes the following fields: aFrame Type field 611 a, a Reserved field 611 b, Number of Entries field611 c, Frame Number field 611 d, Offset Table field 611 e, Padding field611 f, and a Command /Acknowledgment field 611 g. For this type ofpacket 611, the 8-bit Frame Type field 611 a is set to a value of 5. A3-bit Reserved field 611 b is unused and set to 0 for transmission; thefield 611 b is ignored on reception. The Number of Entries field 611 c,a 5-bit field, specifies the number of entries in the Offset Table field611 e. For Acknowledgments, the 16-bit Frame Number field 611 dindicates the frame that is being acknowledged; for Commands, the field611 d specifies the frame that the command is directed towards. TheOffset Table field 611 e (with N×10 bits) provides a table of offsetsfor where each of the variable sized Command/Acknowledgment fields 613begin. The size of the field 611 e is known based on the Command field613, but can also be derived from the Offset for the next Entry, or thesize of the IP Datagram for the last entry. Each offset is a 10 bitvalue, and starts from the beginning of the Offset Table field 611 e.The value of N is the Number of Entries. Padding field 611 f varies inlength from 0 to 6 bits and provides byte alignment at the end of theOffset Table field 611 e. A Command /Acknowledgment field 613 has alength of N×8 bits and provides a list of Commands or Acknowledgments,sorted by serial number (SerNr); these commands and acknowledgements aredefined according to FIGS. 6G-6L. It should be noted that no more thanone Command or Acknowledgment can be sent to an adapter per packet. Thevalue of N is derived from the length of the IP Datagram.

FIG. 6 g shows an Exemplary Ranging Acknowledgement. The acknowledgement613 includes a Serial Number (Serial No.) field 613 a (26 bits), aCommand field 613 b (4 bits), a Reserved field 613 c (3 bits), anInroute Group ID field 613 d (7 bits), an Assign ID field 613 e (16bits), a Power Adjustment field 613 f (8 bits), and a Timing Adjustmentfield 613 g (8 bits). The SerNr field 613 a specifies the serial numberof the IRU 109 a. A value of 0 for the Command field 613 b indicates aRanging (and Nonallocated Ranging) Acknowledgment. When an adapter isusing allocated Ranging, it may not receive Ranging Acknowledgements foreach Frame, but the Encapsulated Datagrams may be acknowledged with theInroute Acknowledgement Packet 609. The Reserved field 613 c is similarto the reserved fields described above. The Inroute Group ID field 613 dindicates the Inroute Group for which future Ranging Bursts may beallocated. The Assign ID field 613 e is used for future BandwidthAllocation Packets 637, whereby future Ranging Bursts may be allocated.If the Assign ID field 613 e has a value of 0, Ranging may beterminated, thereby leaving the adapter inactive. Ranging can also beterminated by the clearing of the Ranging bit in the Burst Allocationfield 605 c, but this should only be done if the Ranging had passed. ThePower Adjustment field 613 f is a signed 8 bit field that specifiespower adjustment in increments of 0.1 dB. The Timing Adjustment field613 g indicates timing adjustments in units of μs.

FIG. 6 h shows the structure of an exemplary Aloha Acknowledgement. Thisacknowledgement 615 includes a Serial Number field 615 a, a Commandfield 615 b, a Reserved field 615 c, an Inroute Group ID field 615 d,and an Assign ID field 615 e. These fields 615, 615 a, 615 b, 615 c, and615 e are similar to the fields 613 a, 613 b, 613 c, 613 d, and 613 e,respectively, of the ranging acknowledgement 613. With this particularacknowledgement, the Command field 615 b is given a value of 1. TheInroute Group ID field 615 d specifies the inroute group that is toreceive future bandwidth allocations. The Assign ID field 615 e is an Idused in future Bandwidth Allocation Packets 637, whereby future Burstsmay be allocated. A value of 0 for the Assign ID field 615 eacknowledges the data without assigning any bandwidth. If any Backlog isadvertised from the Aloha packet, the packets may need to be flushed,since the adapter remains inactive and no synchronization is possible.

FIG. 6 i shows the structure of a Disable ITU command, according to anembodiment of the present invention. A Disable ITU command 617 a SerialNumber field 617 a (26 bits), a Command field 617 b (4 bits), and aReserved field 617 c (3 bits). As with the acknowledgement packets 613and 615, the Serial No. field 617 a stores the serial number of the IRU109 a. For this type of command, the Command field 617 b is assigned avalue of 2. Under this command, the IRU 109 a may not transmit until itreceives another command indicating that the IRU 109 a may transmit.This setting, for example, is stored in nonvolatile memory on the IRU109 a.

FIG. 6 j shows the structure of an Exemplary Start Ranging Command. Thiscommand 619 includes a Serial Number field 619 a (26 bits), a Commandfield 619 b (4 bits), an Invalidate field 619 c (1 bit), a Reservedfield 619 d (3 bits), an Inroute Group ID field 619 e (7 bits), and anAssign ID field 619 f (16 bits). In this case, the Command field 619 bhas a value of 3. If the adapter is inactive, this command 619 may startsending an Nonallocated Ranging packet. An active adapter may beinformed by having Ranging bursts allocated. The 1-bit Invalidate field619 c, if set, indicates that the Adapter may invalidate it's priorRanging Info, and revert to the defaults, before sending it'sNonallocated Ranging packet. The Reserved field 619 d, Inroute Group IDfield 619 e, and Assign ID field 619 f are similar to the fields 615 c,615 d, and 615 e, respectively of acknowledge packet 615.

FIG. 6 k shows the structure of a Go Active Command and a Change InrouteGroup Command. These commands include the following fields: a SerialNumber field 621 a (26 bits), a Command field 621 b (4 bits), a Reservedfield 621 d (3 bits), an Inroute Group ID field 621 e (7 bits), and anAssign ID field 621 f (16 bits). For the Go Active Command, the Commandfield 621 b has a value of 4, while the field 621 b is set to a value of5 for the Change Inroute Group command. In both commands, the Assign IDfield 621 e is used in future Bandwidth Allocation Packets, wherebyfuture Bursts may be allocated. With respect to the Go Active Command,if the Assign ID field 621 f has a value of 0, the data is acknowledgedwithout assigning any bandwidth. If there is any Backlog advertised fromthe Aloha packet, the backlog of packets may need to be flushed, sincethe adapter remains inactive and no synchronization is possible. In thecase of a Change Inroute Group command, an Assign ID field 621 e with a0 value can be used to make an adapter inactive (alternatively, thebandwidth allocation of the adapter is removed).

The structure of a Send Test Pattern Command is shown in FIG. 61. Thiscommand 623 includes a Serial Number field 623 a (26 bits), a Commandfield 623 c (4 bits), a Reserved field 623 d (3 bits), a Pattern field623 d (3 bits), and a Frequency field 623 e (24 bits). With thiscommand, the Command field 623 c has a value of 6. It is noted that thiscommand may inactivate the adapter. The 3-bit Pattern field 623 dspecifies the test patterns that can be programmed from the ITUregisters. If the Pattern field 623 d has a value of 0, then the test isterminated. The test can also be terminated if the Send Test PatternCommand is not repeated within four frame times.

The return channel burst structure may be defined by the burst structurerequired by the Burst Channel Demodulators (BCDs) 411 b. The 64 kbpsOQPSK BCD 411 b utilizes the frame structure, shown below in Table 3.The frame overhead is sized as 2 slots (112 bits) minus the aperturesize. The Aperture size (125 microseconds) is 8 bits.

TABLE 3 Field Bits Microsec. Comments Radio Turn-on 2 31 Continuous Wave55 859 Divided into subparts CW Detect 17 Needed for BCD to determinestart of burst Freq Est 24 Needed for BCD frequency offset estimationalgorithm Freq Proc 3.5 Time for BCD to process frequency estimation HWUpdate 10.5 Time to prepare DSPs and other components for data UniqueWord 24 375 Unique word needed for burst acquisition DeadTime 3 47 All1's PAYLOAD 56*N 875*N Each slot is 7 bytes of user traffic Postamble 18281 Parity bits at the end of the burst Radio Turnoff 2 31 TOTALOverhead 104 2 slots - Aperture (8 bits)

All the fields in the Inroute packets, and Inroute related packets, maybe encoded using a Big Endian (Network Byte Order) format. To be morespecific, the bits in any structure defined for these packets may startwith bit 7 of byte 0, and after reaching bit 0 in each byte, they maywrap into bit 7 of the next byte. When a field has bits crossing overthe byte boundary, the lower numbered bytes may have the higher placevalue. For example if an 13 bit field started on bit 2 of byte 7, thenthe 3 most significant bits (12:10) would come from byte 7 bits 2:0, the8 next most significant bits (9:2) would come from byte 8, and the 2least significant bits (1:0) would come from byte 9 bits 7:6.

As shown in FIG. 6 m, the inroute packet format includes of a variablesize header and 0 or more bytes of encapsulated datagrams. Theencapsulated datagrams are sent as a continuous byte stream ofconcatenated datagrams, with no relationship to inroute packetization.Proper interpretation may require a reliable, ordered processing of alldata bytes exactly once. To resolve problems due to data loss on theinroute, a selective acknowledgement, sliding window protocol may beused. As is the case for such sliding window protocols, the sequencenumber space may be at least twice the window size, and data outside thewindow may be dropped by the receiver.

Since the burst allocations may be of different sizes, and can vary overtime, the windowing may be of a byte level granularity. For the samereasons, retransmissions may be less efficient, as the retransmissionburst may not match the original transmission burst size.

For allocated streams, Inroute burst data may be retransmitted if notacknowledged in the Inroute Acknowledgement Packet for that FrameNumber, or if that Acknowledgement is lost. After, for example, 3retries, the adapter should classify the ITU as non functional and waitfor user intervention.

If synchronization problems are discovered, the NCC 411 a can force theadapter inactive by removing its bandwidth allocation. This may causethe adapter to reset its sequence number and datagram counter to 0, andstart at the beginning of a new datagram. This may also cause theflushing of all Backlogged datagrams in the IRU. Since the sequencenumber is reset every time the adapter goes active, any data sent inAloha or Nonallocated Ranging bursts may be duplicated due toretransmissions, if the acknowledgement is lost.

One of the “features” of the BCDs 411 b is that multiple packets can beconcatenated in a Burst, but if Bits 7:3 of Byte 0 are all 0's, and Bits7:0 of Byte 1 are all 0's, then the BCD 411 b may ignore the rest of theburst. To take advantage of this, when back to back bursts are allocatedto the same adapter, it may not turn off the Radio, and may use thesaved Burst Overhead for extra Payload. This may keep the required 1 to1 mapping of allocated bursts to packets. Also, if the requirement ofavoid 0's at the beginning of the packet is not met, the BacklogIndicator can be.

Active adapters that have no data ready to send may send Inroute packetsof the full allocated burst size without any encapsulated datagrams tomaintain channel utilization, and allow measurement of inroute PER fromthe NCC 411A. This may be replaced to include periodic NetworkManagement packets containing system profiling information.

A burst data frame (i.e., inroute packet) for Aloha (and ranging) burstshas the structure shown in FIG. 6 m. The NCC 411A can detect the type ofburst from the frame numbering information in the packet header. Thestructure for the inroute packet include the following fields: a SerialNumber Low field 625 a, a Backlog Indicator field 625 b, PaddingIndicator field 625 c, Frame Number field 625 d, Burst Number field 625e, a Length FEC field 625 f, a Length field 625 g, a Serial Number Highfield 625 h, a Destination ID field 625 i, a Backlog field 625 j, aPadding field 625 k, an Encapsulated Datagrams field 625 l, and a CRCfield 625 m. The Serial Number Low field 625 a stores the 8 leastsignificant bits of the serial number. The serial number is splitbecause of the BCD requirements with respect to the location of theLength field 625 g and because of the need to have the first 13 bitsnon-zero. The 1-bit Backlog Indicator field 625 b indicates the presenceof the Backlog field. This should always be present for Aloha andNonallocated Ranging bursts. The 1-bit Padding Indicator field 625 cindicates the absence of the Padding field. This field should be encodedas a 0 to indicate padding is present. The reason that this is encodedthis way, is so that the BCD requirement for having 1 of 13 specificbits set can be met. If they are not set, then the packet is alreadypadded, and one byte of padding can be traded for enabling the Backlog.

The Frame Number field 625 d stores the 2 least significant bits of theframe number, and may help the NCC 411A to determine which burst wasreceived. The 4-bit Burst Number field 625 e indicates the burst slotthat the Frame was transmitted in, assisting with identifying that burstas an Aloha type burst. The 8-bit Length FEC field 625 f is the FECvalue for the length, produced via table lookup in software. The 8-bitLength field 625 g is the length of the burst and includes all the bytesstarting with the Backlog Indicator field 625 b through the CRC field625 m. The 8-bit Serial Number High field 625 h stores the 8 mostsignificant bits of the of the Source adapter's serial number. TheDestination ID field 625I specifies the destination hybrid gateway. TheBacklog field 625 j indicate the number of bytes of Backlog that arepresent. It's encoded as a floating point number with a 2 bit exponentfield and a 6 bit mantissa, and may be rounded up by the IRU. The end ofthe Backlog is indicated by 8^(Backlog[7:6])×Backlog[5:0]×2+SeqNr+sizeof the Encapsulated Datagram field. As such, it may include out oforder, acknowledged data. It is only included to indicate increases inthe size of the backlog, as measured from the IRU. The size of thisfield is sufficient for just under 2 seconds at 256 Kbps. The Paddingfield 625 k, if present, has its first byte indicating the total numberof Padding bytes (N); all the other bytes are “Don't Care”. This field625 k is used to allow for stuffing packets to maintain link utilizationwhen no data needs to be transferred, and to allow the padding ofpackets to the minimum burst size for Turbo codes. The N×8-bitEncapsulated Datagrams field 625 l contains 0 or more bytes ofencapsulated datagrams. There is no relationship between IP Datagramboundaries and the contents of this field; i.e., this field 625 l cancontain a section of an IP Datagrams, or multiple IP Datagrams. Thevalue of N can be derived by subtracting the size of the other fields inthe packet from the Length. The CRC field 625 m stores a 16-bit CRC; aburst with an invalid CRC is dropped and statistics retained.

As shown in FIG. 6 n, the structure of another inroute packet includethe following fields: a Sequence Number Low field 627 a, a BacklogIndicator field 627 b, Padding Indicator field 627 c, Frame Number field627 d, Burst Number field 627 e, a Length FEC field 627 f, a Lengthfield 627 g, a Sequence Number High field 627 h, a Backlog field 627 i,a Padding field 627 j, an Encapsulated Datagrams field 627 k, and a CRCfield 627 l. The Sequence Number Low field 627 a stores the 8 leastsignificant bits of the Sequence, and thus, is 8 bits in length. Thesequence number is split off because of a BCD requirement for theplacement of the Length fields 627 f and 627 g as well as the need toavoid all O's in certain bit positions. The 1-bit Backlog Indicatorfield 627 b indicates the presence of the Backlog field. This shouldalways be present for Aloha and Nonallocated Ranging bursts. The 1-bitPadding Indicator field 627 c indicates the absence of the Padding field627 j. This field 627 j should be encoded as a 0 to indicate padding ispresent. The reason that this is encoded this way, is so that the BCDrequirement for having 1 of 13 specific bits set can be met. If they arenot set, then the packet is already padded, and one byte of padding canbe traded for enabling the Backlog.

The Frame Number field 627 d stores the 2 least significant bits of theframe number, and may help the NCC 411 A to determine which burst wasreceived. The 4-bit Burst Number field 627 e indicates the burst slotthat the Frame was transmitted in. With the addition of the Inroute andFrame number it was received on, the NCC 411A may be able to uniquelyidentify the source (SerNr) and destination (DestId). The 8-bit LengthFEC field 627 f is the FEC value for the length, produced via tablelookup in software. The 8-bit Length field 627 g is the length of theburst and includes all the bytes starting with the Backlog Indicatorfield 627 b through the CRC field 627 m. The 8-bit Sequence Number Highfield 627 h stores the 8 most significant bits of the sequence numberfield that is used for the retransmission protocol. This is theSelective Acknowledgement, sliding window, byte address of the firstbyte of the Encapsulated Datagrams field. With a 32 Kbyte window size,this is large enough for 1 second at 256 Kbps. The Backlog field 627 j,Padding field 627 j, Encapsulated Datagrams field 627 k, and CRC field627 m are similar to the fields 625 j, 625 k, 625 l, and 625 m of packet625.

Some of the packets sent to the NCC 411 a do not require an IP header.Therefore, bandwidth savings are made by sending much smaller datagramheaders, as shown in FIG. 60. The packet 629 includes a 4-bit Reservedfield 629 a, which should have a value of 0 during transmission and maybe used to specify Encryption, Compression, or Priority values. ADatagram Counter/CRC field 629 b (12-bits) stores a 12 bit DatagramCounter value, from which a 12 bit CRC can be calculated by software onthis Encapsulated Datagram appended with the SerNr and DestId; and theresult is stored in this field 629 b over the Datagram Counter value.The purpose of this field 629 b is to detect loss of Synchronizationbetween the IRU 109 a and the NCC 411 a, thereby ensuring uncorruptedreassembly, correct source and destination addresses, and no loss ofdatagrams. Failures on this CRC should be considered as asynchronization failure, and the IRU 109 a should be forced to theinactive state by the NCC 411 a, so as to initiate resynchronization.The polynomial to use in calculating this CRC is X¹²+X¹¹+X³+X²+X+1(0xF01), and the preset (initial) value is 0xFFF. The packet 629 alsoincludes a 4-bit Protocol Version field 629 c; this field 629 c may beencoded as 0 to indicate Network Management datagrams. Further, thisvalue may be explicitly prohibited from being sent from the Host driver,for Network Security reasons. Further the packet 629 contains an 8-bitMessage Type field 629 e for specifying the message type, a 16-bitLength field 629 f for indicating the length of the datagram (includingthe header), and a Payload field 629 g, which is a variable length field(N×8 bits). The value of N is the Length field that is present for allPayload formats.

FIG. 6 p shows the inroute payload format for IP datagrams. The datagram631 includes a Reserved field 631 a, a Datagram Counter/CRC field 631 b,and a Protocol Version field 631 c, which are similar to that of thedatagram of FIG. 60. In addition, the datagram 631 contains a HeaderLength field 631 d (4 bits) for storing the IP header length, a Type ofService field 631 e (8 bits) for specifying the type of service, aLength field 631 f (16 bits) for storing the length of the entiredatagram including the header, and a Rest of Datagram field 631 g (N×8bits). Details of the rest of the IP frame are described in IETF(Internet Engineering Task Force) RFC 791, which is incorporated hereinby reference. The value of N is derived from the Length field. It shouldbe noted that the prior header includes the first four bytes of the IPheader.

A number of scenarios exist in which the NCC 411 a may force an adapterto the inactive state. For example, if the NCC 411 a detects asynchronization error with the adapter, arising from errors in theencapsulation layer of the protocol, or by the Protocol Version field629 c and Length field 629 f of the payload 629 g. In addition, if theNCC 411 a receives no Inroute packets with good CRC from the adapter for24 frame times, then the adapter becomes inactive. Also, if the NCC 411a receives no Inroute packets with good CRC containing encapsulateddatagrams for a number of frame times configured at the NCC 411 a. Priorto that, the adapter may have its bandwidth allocation reduced due toinactivity. Inactivity may forced upon the adapter if the NCC 411 areceives Inroute packets with good CRC containing encapsulated datagramsthat have already been acknowledged (out of window or completelyoverlapping prior data) after a configured number of frame times fromwhen it last advancing the SeqNr. This can be due to excessiveretransmissions, or synchronization errors. Lastly, the adapter can bemade inactive through an operator command.

An IRU 109 a may become inactive if the IRU 109 a does not receive anyBandwidth Allocation packets from its current Inroute Group, which hasassigned the IRU 109 a bandwidth for 24 frame times. If the Bandwidthallocation packet is not received, the IRU 109 a may not transmit duringthat Frame, but may consider itself as remaining active. Reception ofexplicit commands from the NOC 113 may also change the state of the IRU109 a from active to inactive. Further, a USB Reset or a USB Suspend maycause the adapter to go inactive, and flush the adapter's Backlog. Theadapter may go active again, based on received messages from the NOC113. Further, the IRU 109 a may become inactive if a the adapter'stransmit path is disabled because of various conditions, for example,loss of FLL lock, loss of Super Frame synchronization, and etc.

Each of the gateways to be supported by the NCC 411 a is configured intothe NCC 411 a. For each gateway ID, the NCC 411 a has the gatewayaddress to gateway IP address mapping. This mapping may be periodicallysent to all of the receivers. The receiver uses the mapping transmissionto determine which gateway id is associated with its gateway IP addressand informs the IRU 109 a which gateway ID to use for inbound messageswhen it first becomes active using an ALOHA burst. This may supportmodes where the gateway IP address is dynamically set at connectionsetup time.

The source address may be the lower 28 bits of the 32 bit transceiverserial number. This is used for packet rebuilding. Messages may be sentby serial number to a receiver for polling, bandwidth allocation, andretransmission support.

The network timing is designed to control the burst timing of a group ofreturn channels, which share the same frame timing. The frame timing isderived from a pulse from the NCC 411A. The NCC 411A allocatesbandwidth, coordinates the aperture configuration, and sends framingpulses to both the BCDs that receive the traffic and to timing unitswhich measure packet delay.

The NOC 113 may provide return channel frame format information onceevery 8 TDMA frames. The TDMA frame time is 45 milliseconds. Therefore,the return channel “super frame” may be defined as 360 milliseconds. Toproperly coordinate the return channel frame timing, additionalinformation is provided to the receiver so that the receiver mayprecisely time its burst transmission time as an offset of the received“super frame”.

Accordingly, the NCC 411 a sends a super frame marker pulse once every360 ms to the timing units 409, and concurrently transmits a super frameIP frame (super frame header) to all IRUs 109 a. A frame pulse is sentto the BCDs 411 b every 45 milliseconds. The delay between the superframe marker pulse and the associated frame pulse is a fixed time, whichis denoted as the “space timing offset”. The space timing offset iscalculated as the maximum round-trip time from the farthest receiverplus two frame times. The two frame times are provided as a buffer toensure that the transceiver has sufficient time to process returnchannel frame format data and to forward the return channel data to thetransmit indoor unit one-half frame time ahead of the frame transmittime. The super frame header is used by every transceiver 109 tosynchronize the start of frame marker to the NCC 411 a super framemarker. However, this information is not sufficient because there is adelay from the time that the NCC 411 a generates the super frame headeruntil the header is received by the receiver.

The super frame header delay encompasses the NOC delay, the transmissiontime to the satellite (from the NOC 113), and the transmission time fromthe satellite to the specific receiver. The transmission time from thesatellite to the specific receiver is a known parameter that isdetermined during ranging. This value can vary slightly due to satellitedrift along the vertical axis. To adjust for this variation, Echo Timingis implemented at the NOC to measure changes in the satellite position.Echo Timing measures both the transmission time from the NOC 113 to thesatellite 107 and the satellite drift from the NOC's position (whichapproximates the drift from the receiver's position). The transceiver109 is unaware of the delay in the NOC 113, which can vary in real-time.Thus, a second IRU 409 d is implemented in the NOC 113 to measure theNOC delay. A pulse is sent to this IRU 409 d when the frame is supposedto be sent, and the IRU 409 d detects when the frame was actually sent.This delay is broadcast in the Frame Time message to all return channelsto adjust for the NOC delay when calculating the actual time of thestart of the super frame.

When the transceiver 109 receives a super frame packet, the transceiver109 time-stamps the packet. This time-stamp is created, for example,using an internal 32-bit counter free-running at 32.768/4 MHz. For thetransceivers 109 to determine exactly when the super frame markeroccurred at the outroute hub, software of the user terminal 101subtracts the site's satellite delay and the NOC delay. The NOC delay isbroadcast in the Frame Numbering Packet. This delay is calculated at theHUB by the Local Timing IRU. The NOC 113 also provides the NOC 113 tosatellite portion of the satellite delay in this message as thedifference between the local timing and echo timing IRUs 409. TheReceiver has a configured value for the satellite to receiver satellitedelay; other than ranging, this is a fixed value. In this situation, theNOC delay at ranging is stored and the change in the NOC delay is alsoapplied to the receiver satellite delay to approximate satellite drift.When ranging, the PC approximates this value from the location of thesatellite, location of the receiver, NOC timing, and the space timingoffset configured in the NOC. The ranging process adjusts this value,and the site stores the final value.

Once the super frame timing has been generated, the site may determineits transmission time such that the frame is received at the proper timeat the NOC 113. The time at which the site may transmit is a satellitehop prior to the time that the NOC 113 expects the data to be received.The transmission time is measured by starting with the fixed spacetiming offset later than the regenerated super frame time. The NOC delayand the receiver satellite delay may be subtracted from this timebase.The final adjustment, for satellite drift, is made by determining theNOC delay difference between current and ranging and applying it.

The “ranging” process, whereby a site on a NCC 411 a is configured isdescribed as follows. When the IRU 109 a is configured, the host PC 101provides parameters including a “range timing offset” for the receiver.At this point in time, the IRU 109 a may not enable transmission if theranging timing is zero. The IRU 109 a, however, may enable the MAC forthe NCC 411 a master list and receive this message locally. Thereafter,when IRU 109 a acquires transmit timing and is requested by the PC host101 to range, IRU 109 a may select a NCC 411 a based on having anavailable ranging burst. IRU 109 a requests a ranging transmission bysending a message over the ranging burst using some default amount ofpower after some random number of frame backoffs. If no response isreceived and the burst is still available, IRU 109 a may increase powerand try again. If the burst is now allocated to a different user, IRU109 a may revert to selecting a NCC 411 a based on available rangingbursts. Once ranging response is received, IRU 109 a may start sendingranging data every frame; this data may include the frame number. Next,IRU 109 a adjusts ranging time and power based on NOC response andcontinues to adjust until IRU 109 a is within a close tolerance. IRU 109a then stores the values when ranging is successful. IRU 109 a thenenables normal transmission mode.

The NCC 411 a may be capable of requesting a site to enter ranging mode.When the site does enter this mode, the site may use the ranging burstit has been assigned. It may transmit normal traffic (or a smallfill-type packet) to the NCC 411 a. The NCC 411 a may adjust the timingand power for the site. These adjustments may be stored if the NCC 411 aindicates a successful re-range of the site.

According the one embodiment of the present invention, the ReturnChannel requirements are largely based on a traffic model, which definesthe traffic pattern for a typical user. The capacity requirements, forexample, may be as follows. It is assumed that the system 100 is basedon a 2-to-1 ratio of outroute transponders to return channeltransponders. An exemplary requirement is approximately 22,000 users pertransponder, so 45,000 users (4500 active) per transponder are requiredfor the return channel. Given a 2-to-1 ratio, 300 64 kbps returnchannels per transponder are supported by system 100, with 15 activeusers per return channel. Each NCC 411 a supports up to 30 returnchannels (32 BCDs, in which 2 are backups). Since each return channelsupports 15 active users, the bandwidth sizing may assume 450 activeusers for a NCC 411 a. The return channels may be scaled in sets of 30return channels.

In the alternative, the system 100 may support a 5-to-1 ratio ofoutroute transponders to return channel transponders. In this case, thesystem 100 provides up to 600 64 kbps return channels per transponder,with 25 active users per return channel

The return channels on an NCC 411 a, according to an embodiment of thepresent invention, may support frequency hopping to provide increasedefficiency of system 100. A subset of return channels may be configuredto support a contention protocol, such as Aloha. It should be noted thatany equivalent contention protocol may be utilized in system 100. Areceiver may randomly select a return channel with Aloha slots. In turn,the NOC 113 may assign the receiver a stream on the same or a differentreturn channel. The NOC 113 may change the frequency for the assignedstream when the site requires additional bandwidth, when another siterequires additional bandwidth on the same return channel, or when thesite may be used for a poll response on another return channel to keepthe BCD 411 b locked for the return channel. NCC polling is used to keepBCDs 411 b locked. The NCC polling algorithm also ensures that bandwidthis not wasted polling sites that are known to be either good or bad. TheNCC polling algorithm may poll sites based on a LRU used list. Both theleast recently used and “known bad” list may be rolled through toperiodically verify site health of all sites. When the NCC 411 a changesthe frequency for a site, the NCC 411 a may, at a minimum, provide asingle frame for the site to retune to the new frequency.

A user on the system may have bandwidth allocated in one of thefollowing three states. In the first state, if the user has nottransmitted traffic for a period of time, then the user may be inactive.When inactive, the user may use Aloha to send initial traffic to the NOC113. The second state is when the user is active. In this state, aperiodic stream is setup for the user. The periodic stream, at 1 kbps,is sufficient to handle TCP acknowledgements assuming ack reductiontimer of 400 milliseconds. In the third state, the user's transmitbacklog exceeds a predetermined value, in which additional bandwidth isprovided. Additional bandwidth allocations are supplied until themaximum is attained or the backlog begins to decrease.

A pure-Aloha system assumes that a packet is randomly transmitted in aslot when data transmission is requested. The standard efficiency of apure-Aloha system is 7%; this means that, when over 7% of the system isloaded, there may be a high number of retransmits necessary, making theresponse time delays too long. With a 7% efficiency rate, each activeuser would get (64 kbps/return channel)*(1 return channel/15users)*(0.07)=300 bits/sec. This is obviously not enough bandwidth. Inaddition, aloha return channels may have more difficulty applying futureefficiency techniques because of the collision nature of the channel.

A diversity aloha system is an adjustment to the pure-aloha system inthat every packet to be sent is actually sent 3 times. This channelbecomes 14% efficient. This doubles the throughput to 601 bits/sec.

An Aloha/Periodic stream technique is based upon the idea of being ableto forecast the type of traffic an active user may be transmitting overthe return channel. For the forecasted traffic (which occurs a majorityof the time), the user may have non-collision bandwidth available. Whenthe traffic requirements exceed the forecasted level, the user may beprovided with additional allocated bandwidth.

An Aloha/Periodic Stream—PLUS technique builds upon the aboveAloha-based concepts. Some of the capabilities that are provided inaddition to the periodic stream are as follows: load balancing andminimal delay. The traffic is balanced to ensure that non-busy user(those not requiring additional bandwidth) are equally loaded on allreturn channels that support the streams. Also, a minimal delayalgorithm, which is more fully described below, is employed to ensurethat user traffic can be transmitted to the NOC 113 expediently.

The minimal delay approach relies on equally dividing all bandwidth,other than that used for users requiring additional bandwidth, among allother active users. A minimum (4 kbps or so) may be ensured for eachuser so other users may be unable to request additional bandwidth ifevery site does not have the minimum amount of bandwidth. This approachprovides optimal results when the return channels are lightly loaded. Asusers become active, they are assigned to the return channels with thefewest number of users which leads to automatic load balancing.

In addition, some minimal burst size is defined for the per-user burst.This size results in a maximum number (denoted as M) of bursts per frame(which may be 3 (120 byte)−5 (71 bytes)) depending of frame analysis. Ona given return channel, it is assumed that there are 357 burst bytes perframe time, which may be at least two bursts of traffic. As users areassigned to the return channel, they are provided bandwidth according toTable 4, below.

TABLE 4 No. of Users Burst/frame Approximate Rate 1 user Twobursts/frame 90% 2 users One burst/frame 45% 3-M users One burst/frame[0.90/(3-M)] × 100% M + 1-2M users One burst/frame [0.90/(M + 1-2M)] ×100% 2M + 1-4M users One burst/frame [0.90/(2M + 1-4M)] × 100%

If M is defined as 5, then up to 20 users may be supported with eachuser getting 2.5 kbps. If M is defined as 4, then the number of userssupported per return channel is 16 which is above the required value.

The bandwidth allocation is based on pre-defining the size of the“periodic” burst. According to one embodiment of the present invention,it is assumed that three equally-sized bursts may be used. Since the 64kbps frame has 57 7-byte slots, each burst may have a size of 19×7=133bytes.

The algorithm also assumes a small number of return channels which arefull of slotted Aloha slots. These slots may be sized to handle thenormal first transmission from a user (which is either a DNS lookup oran actual request). The Aloha burst sizes may be also 98 bytes (14slots) to support 4/frame. Fine tuning may be required using an ERLANGanalysis on the arrival rate of packets from receivers in an inactivestate.

When an Aloha burst is received, the user is assigned periodicbandwidth. The bandwidth is given an inactivity timeout value inseconds. In particular, if no data are yet received for the user, thealgorithm uses the configured long timeout. If past data indicatesperiodic individual packets, the configured short timeout is used;otherwise, the long timeout is employed.

When a receive packet indicates that the backlog is greater than aconfigured amount, additional bandwidth may be provided to ensure thatthe data can be transmitted within a configured amount of time, ifsufficient bandwidth exists. This may require switching the user toanother return channel.

The bandwidth allocation algorithm ensures, when possible, that only theperiodic bandwidth users are moved to another frequency. This allows thehigh-throughput users to transmit with no single frames of downtime(which are required if the site must switch frequencies). When possible,the bandwidth is allocated to ensure that user traffic backlog isreduced within a certain number of frames. The total backlog above theamount needed for additional bandwidth is determined. The algorithmdetermines if the requested bandwidth can be met within the number offrames. If so, the bandwidth is allocated as needed; if not, then thealgorithm starts by limiting the bandwidth for those users with thelargest backlog, as more fully described below.

FIG. 7 shows a flow chart of the return channel bandwidth limitingprocess utilized in the system of FIG. 1. Bandwidth limiters are used insystem 100 to ensure that a user does not monopolize bandwidth, therebymaintaining fairness in manner bandwidth is allocated. The totalbandwidth allocated to a specific user may be limited by a fixed amountof bandwidth every frame. In step 701, the transceivers 109 provide theNOC 113 with information on the amount of backlog that the transceivers109 possess. The NOC 113, as in step 703, assigns a predeterminedminimum amount of bandwidth to each of the active users. This minimumvalue is configurable depending on the capacity of the system 100 andthe number of user terminals 101. Next, the NOC 113 determines whetherexcess bandwidth is available, per step 705. If bandwidth is available,the NOC 113 checks whether the system can honor all of the bandwidthrequirements (as indicated by the backlog information) (step 707). Ifthere is insufficient bandwidth available to satisfy all the outstandingrequests (i.e., backlog), then the NOC 113 determines the backlog thatis next to the highest backlog, per step 709. It should be noted thatduring step 707, the users' requests using the greatest backlog as thethreshold could not be met; according another threshold is defined basedupon this next largest backlog value (step 111). Steps 707-711 arerepeated until a threshold is reached in which some (or all) of theusers' backlogs are satisfied across the entire span of users. At whichtime, the NOC 113 allocates bandwidth to the users, as in step 713,based upon the modified threshold. This approach advantageously ensuresthat all users receive a minimum amount of bandwidth before highbandwidth users are further bandwidth allocations.

Alternatively, another approach to limit bandwidth is to limit protocolssuch as ICMP so a user cannot monopolize a channel with PINGs.

FIG. 8 is a flow chart of the auto-commissioning process utilized in thesystem of FIG. 1. The auto-commissioning process enables the user to beon-line with the system 100 through an automated process that obtain thenecessary configuration parameters for the transceiver 109 and ODU 307.The transmit path may be configured through a utility which savestransmission parameters to the PC 101, allows frame timing fine-tuning(referred to as “ranging”), and provides troubleshooting tools for thetransmission portion (i.e., ITU 109 b) of the transceiver 109. Thesystem 100 provides autocommissioning without requiring a phone line.The purpose of auto-commissioning is to prepare the system to beoperational.

A user may commission the two-way site with no access to a phone line orto the Internet 105. In step 801, the user installs software in the PC101. The PC 101 executes the auto setup program, as in step 803. Forexample, when the user starts the setup program from a CD (compactdisc), the user may enter location information. To be as user-friendlyas possible, the information may be in terms of country, state/province(optional), and city. From this information, the PC 101 may estimate thelatitude and longitude of the site and select a two-way “beacon” for thesite based upon the information on the CD. The program instructs, as instep 805, the user to point the antenna to the beacon satellite usingpredefined pointing values. The system 100 provides a default satellite107 and associated default transponder, whereby a user terminal 101undergoing the commissioning process may establish communication withthe NOC 113.

Upon a successful antenna pointing (and ranging), a temporary channel isestablished, as in step 807, from the transceiver 109 to the NOC 113 viasatellite 107. This temporary channel may support either aconnection-oriented or connectionless (e.g., datagram) connection.According to one embodiment of the present invention, the temporarychannel carries TCP/IP traffic, thereby permitting the use of auser-friendly web access and file transfer capabilities. The softwaremay be capable of communicating over the system 100 to an“auto-commissioning server” in the NOC 113 to perform the two-wayinteraction required to sign the user up for two-way access.

In step 809, the NOC 113 collects user information, such as billing andaccounting information, user antenna location, and service planselection. Next, the NOC 113 downloads the network configurationparameters, antenna pointing parameters, and transceiver tuningparameters to the PC 101, per step 811. According to one embodiment ofthe present invention, the antenna pointing parameters include thefollowing: satellite longitude (East or West), satellite longitude,satellite polarization, satellite polarization offset, and satellitefrequency. The transceiver parameters may include a symbol rate,modulation type, framing mode, Viterbi mode, and scramble mode. Next,the PC 101 is configured based upon the received network configurationparameters (step 813). In step 815, the user performs the antennapointing process, as instructed by the program; this process is morefully described below with respect to FIG. 9. Thereafter, the PC 101sets various other parameters relating to PC system settings, per step817 (e.g., default directories for loading packages) and desiredapplications (e.g., webcast, newscast, etc.).

FIG. 9 is a flow chart of the antenna pointing operation associated withthe auto-commission process of FIG. 8. In step 901, the user enters thelocation of the antenna by specifying the ZIP code, for example. Basedupon the ZIP code, the setup program displays the antenna pointingdetails, per step 903. The user then points the antenna, as in step 905,according to the antenna pointing details. Pointing involves physicallydirecting the antenna assembly according to the parameters that aresupplied by the setup program. For example, the bolts in the antennaassembly may be tightened enough so that the antenna does not move,except the azimuth (horizontally around the pole). The user may adjustthe elevation by 0.5 degrees every 2 seconds until the elevation ismaximized. Next, the azimuth is gradually moved (1 degree per second)until it is maximized.

The program indicates whether the antenna is pointed to the correctsatellite (step 907). If the antenna is not pointed to the correctsatellite 107, then the user adjusts the antenna position, per step 909.The user checks whether the antenna is properly position to exhibit anacceptable signal strength, as indicated by the setup program (step911). This measurement provides digital signal strength for ademodulated carrier. If the signal strength is below an acceptablelevel, then the user must re-adjust the antenna (step 909). Thisapproach requires another person to read the PC Antenna pointing screenwhile the antenna is adjusted; alternatively, the user may listen to anaudible tone. Upon obtaining an acceptable signal strength, the antennaprocess ends.

As part of this process, the user may be assigned to a service that maybe supported on a different satellite or the same satellite. If theservice is on a different satellite, the user may re-point to anothersatellite and then should automatically be ranged and obtain service.

The IRU 109 a supports an AGC (automatic gain control) circuitry inaddition to the signal quality factor measurement. The AGC circuitryprovides a raw signal strength measurement that indicates that thereceiver is receiving energy from a satellite 107. This provides theadditional advantage that the signal can be measured prior to thedemodulator being locked. However, the circuitry may lead to pointing tothe wrong satellite if a nearby satellite has a carrier at the samefrequency to which the receiver is tuning to lock to a carrier.

The antenna pointing for the IRU 109 a is supported in two differentmodes. Using voltage emitted from the ODU 307. It requires installationof the transmission equipment, and requires that the user have avoltmeter that can be attached to the ODU 307. The second mode is to usea PC Antenna pointing program, which may be separate from theauto-commissioning setup program. This is the approach used when theuser either does not have transmission equipment or does not have avoltmeter to attach to the transmit ODU.

The first approach allows a user to be physically present at theantenna, without interaction with the PC while pointing the antenna.This approach assumes that IRU 109 a, ITU 109 b, power supply 109 c,dual IFL 303, and ODU 307 have been properly installed. A voltmeter thatmeasures, for example, 0-10 volts may be used.

The user performing the antenna pointing process may start the pointingprogram from the host PC 101. This software places the equipment in amode where, instead of transmitting any user traffic, it places thetransmission equipment in a mode where voltage is supplied to the ODU307 to emit on an F-connector on the back of the ODU 307. This programalso supplies an approximation of the pointing parameters for theantenna. These values should be written and used to point the ODU. Thevoltage on the F-connector can interpreted as follows. The voltage rangeof 0-4V indicates an AGC level. The higher the voltage, the stronger thesignal. When the voltage is in this range, the modulator is not locked.If the signal remains over 3V for over 10 seconds, then it is likelythat the antenna is pointed to the wrong satellite. A voltage of 5Vindicates a lock to an outroute that does not match the commissionedcharacteristics. The most probable cause is pointing to an incorrect,adjacent satellite, which can be corrected by minor azimuth changes. Thevoltage range of 6-10V specifies an SQF Value, in which the higher thevoltage, the stronger the signal. A value of 8.0 may equate to an SQF of100, which is the minimal acceptable level for an installation.

FIG. 10 is a diagram showing the scalability of the system of FIG. 1.The system 100, according to an embodiment of the present invention, canscale to accommodate millions of customers. Conceptually, the resourcesof the system 100 is subdivided numerous times until a small number ofusers are sharing a small number of resources. The layers to scaling areas follow: (1) system, (2) transponder-sets, (3) Return ChannelEquipment, and (4) Return Channel. At the system layer, an extremelylarge number of users can be supported. For the transponder-sets, two ormore outroutes may be supported; therefore, more than two sets of ReturnChannel Equipment 411 are used at this layer. The transponder set alsoincludes the necessary equipment to support a transponder's worth ofreturn channels, supporting up to 100,000 users. At the Return ChannelEquipment layer, which includes up to 31 return channels, a set of usersare configured to each set of RCE 411 during ranging time. Thisconfiguration may also be dynamically switched. At the Return Channellayer, when a user becomes active, the user may be assigned bandwidth ona specific return channel. Up to 16 active users may be supported per 64kbps return channel.

The above scalable configuration is described from a “bottom up” pointof view, starting with the return channel to the system level. TheReturn Channel uplink is a standard NOC 113 with the additional timingunit equipment required to perform timing on each transponder. This mayrequire the standard NOC infrastructure, including hybrid gateways,satellite gateways, and uplink redundancy. In addition, a Portion of onerack for additional equipment is required. Two Timing Units are used peruplink transponder (each with 2 IRUs). A System IF Distribution module403 to distribute return channel signal to the RCE sets. A portmastermay also be needed to support the serial connections to do monitor andcontrol of the 10 sets of BCDs. It should be noted that RS232limitations may require the portmaster to be within 60 feet of all RCEequipment sets.

The return channel equipment 411 receives the data from the returnchannels and prepares the packets to be sent to the appropriate hybridgateways 419. The Return Channel Equipment 411 includes the followingfor 30 return channels: 3 BCD Racks; 8 BCD Chassis, each with 4 powersupplies; cards required to properly connect 8 BCD chassis to theNC-Bus, Redundancy Bus, and M&C Bus; Network IF Distribution; 32 sets ofBCD equipment; and two NCCs 411 a (e.g., PCs with TxRx).

FIG. 11 is a diagram of a computer system that can execute and supportthe system interfaces and protocols of system 100, in accordance with anembodiment of the present invention. Computer system 1101 includes a bus1103 or other communication mechanism for communicating information, anda processor 1105 coupled with bus 1103 for processing the information.Computer system 1101 also includes a main memory 1107, such as a randomaccess memory (RAM) or other dynamic storage device, coupled to bus 1103for storing information and instructions to be executed by processor1105. In addition, main memory 1107 may be used for storing temporaryvariables or other intermediate information during execution ofinstructions to be executed by processor 1105. Computer system 1101further includes a read only memory (ROM) 1109 or other static storagedevice coupled to bus 1103 for storing static information andinstructions for processor 1105. A storage device 1111, such as amagnetic disk or optical disk, is provided and coupled to bus 1103 forstoring information and instructions.

Computer system 1101 may be coupled via bus 1103 to a display 1113, suchas a cathode ray tube (CRT), for displaying information to a computeruser. An input device 1115, including alphanumeric and other keys, iscoupled to bus 1103 for communicating information and command selectionsto processor 1105. Another type of user input device is cursor control1117, such as a mouse, a trackball, or cursor direction keys forcommunicating direction information and command selections to processor1105 and for controlling cursor movement on display 1113.

According to one embodiment, interaction within system 100 is providedby computer system 1101 in response to processor 1105 executing one ormore sequences of one or more instructions contained in main memory1107. Such instructions may be read into main memory 1107 from anothercomputer-readable medium, such as storage device 1111. Execution of thesequences of instructions contained in main memory 1107 causes processor1105 to perform the process steps described herein. One or moreprocessors in a multi-processing arrangement may also be employed toexecute the sequences of instructions contained in main memory 1107. Inalternative embodiments, hard-wired circuitry may be used in place of orin combination with software instructions. Thus, embodiments are notlimited to any specific combination of hardware circuitry and software.

Further, the instructions to support the system interfaces and protocolsof system 100 may reside on a computer-readable medium. The term“computer-readable medium” as used herein refers to any medium thatparticipates in providing instructions to processor 1105 for execution.Such a medium may take many forms, including but not limited to,non-volatile media, volatile media, and transmission media. Non-volatilemedia includes, for example, optical or magnetic disks, such as storagedevice 1111. Volatile media includes dynamic memory, such as main memory1107. Transmission media includes coaxial cables, copper wire and fiberoptics, including the wires that comprise bus 1103. Transmission mediacan also take the form of acoustic or light waves, such as thosegenerated during radio wave and infrared data communication.

Common forms of computer-readable media include, for example, a floppydisk, a flexible disk, hard disk, magnetic tape, or any other magneticmedium, a CD-ROM, any other optical medium, punch cards, paper tape, anyother physical medium with patterns of holes, a RAM, a PROM, and EPROM,a FLASH-EPROM, any other memory chip or cartridge, a carrier wave asdescribed hereinafter, or any other medium from which a computer canread.

Various forms of computer readable media may be involved in carrying oneor more sequences of one or more instructions to processor 1105 forexecution. For example, the instructions may initially be carried on amagnetic disk of a remote computer. The remote computer can load theinstructions relating to the system interfaces and protocols of system100 remotely into its dynamic memory and send the instructions over atelephone line using a modem. A modem local to computer system 1101 canreceive the data on the telephone line and use an infrared transmitterto convert the data to an infrared signal. An infrared detector coupledto bus 1103 can receive the data carried in the infrared signal andplace the data on bus 1103. Bus 1103 carries the data to main memory1107, from which processor 1105 retrieves and executes the instructions.The instructions received by main memory 1107 may optionally be storedon storage device 1111 either before or after execution by processor1105.

Computer system 1101 also includes a communication interface 1119coupled to bus 1103. Communication interface 1119 provides a two-waydata communication coupling to a network link 1121 that is connected toa local network 1123. For example, communication interface 1119 may be anetwork interface card to attach to any packet switched local areanetwork (LAN). As another example, communication interface 1119 may bean asymmetrical digital subscriber line (ADSL) card, an integratedservices digital network (ISDN) card or a modem to provide a datacommunication connection to a corresponding type of telephone line.Wireless links may also be implemented. In any such implementation,communication interface 1119 sends and receives electrical,electromagnetic or optical signals that carry digital data streamsrepresenting various types of information.

Network link 1121 typically provides data communication through one ormore networks to other data devices. For example, network link 1121 mayprovide a connection through local network 1123 to a host computer 1125or to data equipment operated by a service provider, which provides datacommunication services through a communication network 1127 (e.g., theInternet). LAN 1123 and network 1127 both use electrical,electromagnetic or optical signals that carry digital data streams. Thesignals through the various networks and the signals on network link1121 and through communication interface 1119, which carry the digitaldata to and from computer system 1101, are exemplary forms of carrierwaves transporting the information. Computer system 1101 can transmitnotifications and receive data, including program code, through thenetwork(s), network link 1121 and communication interface 1119.

The techniques described herein provide several advantages over priorapproaches to providing access to the Internet. A receiving unit isconfigured to receive data from a user terminal. A transmitting unit iscoupled to the receiving unit and configured to transmit the data to anantenna. The data is transmitted over a return channel that isestablished over the satellite to a hub; the hub has connectivity to apacket switched network. This approach advantageously provides a modularapproach to upgrading from a receiving only system to a two-way system.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. An apparatus for transmitting and receiving signals over a two-waysatellite communication system, comprising: a receiving unit configuredto receive TCP/IP data from a user terminal; and a transmitting unitcoupled to the receiving unit and configured to transmit the data to anantenna, wherein said transmitting unit receives network managementinstructions from a hub operatively coupled to a packet switchednetwork, and prepares transmission data in accordance with saidinstructions, wherein the data is transmitted over a return channel thatis established over a satellite to the hub, and wherein said hub managesthe return channel bandwidth during transmission.
 2. The apparatusaccording to claim 1, wherein the receiving unit is dynamicallyconnected to the user terminal via a Universal Serial Bus (USB)connection.
 3. The apparatus according to claim 1, further comprising: apower supply configured to provide power to the receiving unit.
 4. Theapparatus according to claim 3, wherein the receiving unit forwards thedata to the transmitting unit via a cable, the cable providing power tothe transmitting unit.
 5. The apparatus according to claim 4, whereinthe cable is a serial data link.
 6. The apparatus according to claim 1,wherein the transmitting unit and the receiving unit are connected to alow noise block via a common cable, the low noise block being mounted onan elliptical antenna.
 7. The apparatus according to claim 1, whereinthe transmitting unit is a peripheral device to the receiving unit. 8.The apparatus according to claim 1, wherein the packet switched networkis an IP (Internet Protocol) network.
 9. A system for exchanging signalsover a two-way satellite network, comprising: an indoor receiving unit(IRU) configured to receive TCP/IP data from a user terminal; an indoortransmitting unit (ITU) selectively coupled to the receiving unit andconfigured to transmit the data wherein said ITU receives networkmanagement instructions from a hub, operatively coupled to a packetswitched network, and prepares transmission data in accordance with saidinstructions; and an outdoor unit (ODU) coupled to the IRU and ITU andconfigured to receive the data for transmission over a return channelthat is established over a satellite to the hub, wherein said hubmanages the return channel bandwidth during transmission.
 10. The systemaccording to claim 9, wherein the IRU is dynamically connected to theuser terminal via a Universal Serial Bus (USB) connection.
 11. Thesystem according to claim 9, further comprising: a power supplyconfigured to provide power to the IRU.
 12. The system according toclaim 11, wherein the IRU forwards the data to the ITU via a cable, thecable providing power to the ITU.
 13. The system according to claim 12,wherein the cable is a serial data link.
 14. The system according toclaim 9, wherein the ITU and the IRU are connected to the ODU via acommon cable.
 15. The system according to claim 9, wherein the ITU is aperipheral device to the IRU, the ITU being contained in a housing thatis separate housing from the IRU.
 16. The system according to claim 9,wherein the ODU comprises: an antenna configured to transmit and receivesignals from the satellite; a low noise block mounted on the antenna;and a radio coupled to the low noise block and configured to receive thedata from the ITU and to transmit signals to the IRU.
 17. The systemaccording to claim 9, wherein the packet switched network is an IP(Internet Protocol) network.